hopefully fix crash in constraints (microsoft#60)

fixes microsoft#17269

src/vcpkg/dependencies.cpp

@@ -1481,7 +1481,18 @@ namespace vcpkg::Dependencies
  }
 
  auto& dep_node = emplace_package(dep_spec);
- add_constraint(dep_node, dep, ref.first.name());
+ if (dep_spec == ref.first)
+ {
+ // this is a feature dependency for oneself
+ for (auto&& f : dep.features)
+ {
+ add_constraint(ref, f, ref.first.name());
+ }
+ }
+ else
+ {
+ add_constraint(dep_node, dep, ref.first.name());
+ }
 
  p.first->second.emplace_back(dep_spec, "core");
  for (auto&& f : dep.features)