Crash clustering an empty feature collection

[1ec5]

Clustering an empty feature collection leads to a crash in kdbush:

Thread 1Queue : com.apple.main-thread (serial)
#0	0x00000001055dd7da in void kdbush::KDBush<mapbox::supercluster::Cluster, unsigned int>::select<(unsigned char)0>(unsigned int, unsigned int, unsigned int) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/kdbush/0.1.1/include/kdbush.hpp:176
#1	0x00000001055dc131 in kdbush::KDBush<mapbox::supercluster::Cluster, unsigned int>::sortKD(unsigned int, unsigned int, unsigned char) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/kdbush/0.1.1/include/kdbush.hpp:154
#2	0x00000001055dbf5c in void kdbush::KDBush<mapbox::supercluster::Cluster, unsigned int>::fill<std::__1::__wrap_iter<mapbox::supercluster::Cluster const*> >(std::__1::__wrap_iter<mapbox::supercluster::Cluster const*> const&, std::__1::__wrap_iter<mapbox::supercluster::Cluster const*> const&) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/kdbush/0.1.1/include/kdbush.hpp:63
#3	0x00000001055da958 in kdbush::KDBush<mapbox::supercluster::Cluster, unsigned int>::fill(std::__1::vector<mapbox::supercluster::Cluster, std::__1::allocator<mapbox::supercluster::Cluster> > const&) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/kdbush/0.1.1/include/kdbush.hpp:46
#4	0x00000001055da5de in mapbox::supercluster::Supercluster::Zoom::Zoom(mapbox::geometry::feature_collection<double, std::__1::vector> const&) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/supercluster/0.2.0/include/supercluster.hpp:167
#5	0x00000001055da03d in mapbox::supercluster::Supercluster::Zoom::Zoom(mapbox::geometry::feature_collection<double, std::__1::vector> const&) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/supercluster/0.2.0/include/supercluster.hpp:159
#6	0x00000001055d8f9f in std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>::pair<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&, void>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:318
#7	0x00000001055d8f7a in std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>::pair<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&, void>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:319
#8	0x00000001055d8f66 in void std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> >::construct<std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>, int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>*, int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1740
#9	0x00000001055d8f39 in void std::__1::allocator_traits<std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> > >::__construct<std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>, int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(std::__1::integral_constant<bool, true>, std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> >&, std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>*, int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1656
#10	0x00000001055d8ef9 in void std::__1::allocator_traits<std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> > >::construct<std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>, int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> >&, std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom>*, int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1502
#11	0x00000001055d8eb6 in std::__1::unique_ptr<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*>, std::__1::__hash_node_destructor<std::__1::allocator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*> > > > std::__1::__hash_table<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::__unordered_map_hasher<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::hash<unsigned char>, true>, std::__1::__unordered_map_equal<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::equal_to<unsigned char>, true>, std::__1::allocator<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom> > >::__construct_node<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__hash_table:2259
#12	0x00000001055d7cfa in std::__1::pair<std::__1::__hash_iterator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*>*>, bool> std::__1::__hash_table<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::__unordered_map_hasher<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::hash<unsigned char>, true>, std::__1::__unordered_map_equal<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::equal_to<unsigned char>, true>, std::__1::allocator<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom> > >::__emplace_unique_impl<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__hash_table:2046
#13	0x00000001055d7cb4 in std::__1::pair<std::__1::__hash_iterator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*>*>, bool> std::__1::__hash_table<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::__unordered_map_hasher<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::hash<unsigned char>, true>, std::__1::__unordered_map_equal<unsigned char, std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, std::__1::equal_to<unsigned char>, true>, std::__1::allocator<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom> > >::__emplace_unique<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__hash_table:1078
#14	0x00000001055d7c7c in std::__1::pair<std::__1::__hash_map_iterator<std::__1::__hash_iterator<std::__1::__hash_node<std::__1::__hash_value_type<unsigned char, mapbox::supercluster::Supercluster::Zoom>, void*>*> >, bool> std::__1::unordered_map<unsigned char, mapbox::supercluster::Supercluster::Zoom, std::__1::hash<unsigned char>, std::__1::equal_to<unsigned char>, std::__1::allocator<std::__1::pair<unsigned char const, mapbox::supercluster::Supercluster::Zoom> > >::emplace<int, mapbox::geometry::feature_collection<double, std::__1::vector> const&>(int&&, mapbox::geometry::feature_collection<double, std::__1::vector> const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/unordered_map:916
#15	0x00000001055d7c44 in mapbox::supercluster::Supercluster::Supercluster(mapbox::geometry::feature_collection<double, std::__1::vector> const&, mapbox::supercluster::Options) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/supercluster/0.2.0/include/supercluster.hpp:96
#16	0x00000001055d7908 in mapbox::supercluster::Supercluster::Supercluster(mapbox::geometry::feature_collection<double, std::__1::vector> const&, mapbox::supercluster::Options) at /Users/mxn/hub/mapbox-gl-native-2/mason_packages/headers/supercluster/0.2.0/include/supercluster.hpp:90
#17	0x0000000105593471 in std::__1::__unique_if<mapbox::supercluster::Supercluster>::__unique_single std::__1::make_unique<mapbox::supercluster::Supercluster, mapbox::geometry::feature_collection<double, std::__1::vector> const&, mapbox::supercluster::Options&>(mapbox::geometry::feature_collection<double, std::__1::vector> const&&&, mapbox::supercluster::Options&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:3141

/ref mapbox/mapbox-gl-native#7622 (comment)
/cc @mourner @jfirebaugh

[mourner]

Addressed in mourner/kdbush.hpp@1e22d35

[mourner]

#19