fix ForwardIterator reference to temporary object

[ajkr]

Fixes the following ASAN error:

==2108042==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fc50ae9b868 at pc 0x7fc5112aff55 bp 0x7fff9eb9dc10 sp 0x7fff9eb9dc08
=== How to use this, how to get the raw stack trace, and more: fburl.com/ASAN ===
READ of size 8 at 0x7fc50ae9b868 thread T0
SCARINESS: 23 (8-byte-read-stack-use-after-scope)
     #0 rocksdb/dbformat.h:164                   rocksdb::InternalKeyComparator::user_comparator() const
     #1 librocksdb_src_rocksdb_lib.so+0x1429a7d  rocksdb::RangeDelAggregator::InitRep(std::vector<...> const&)
     #2 librocksdb_src_rocksdb_lib.so+0x142ceae  rocksdb::RangeDelAggregator::AddTombstones(std::unique_ptr<...>)
     #3 librocksdb_src_rocksdb_lib.so+0x1382d88  rocksdb::ForwardIterator::RebuildIterators(bool)
     #4 librocksdb_src_rocksdb_lib.so+0x1382362  rocksdb::ForwardIterator::ForwardIterator(rocksdb::DBImpl*, rocksdb::ReadOptions const&, rocksdb::ColumnFamilyData*, rocksdb::SuperVersion*)
     #5 librocksdb_src_rocksdb_lib.so+0x11f433f  rocksdb::DBImpl::NewIterator(rocksdb::ReadOptions const&, rocksdb::ColumnFamilyHandle*)
     #6 rocksdb/src/include/rocksdb/db.h:382     rocksdb::DB::NewIterator(rocksdb::ReadOptions const&)
     #7 rocksdb/db_range_del_test.cc:807         rocksdb::DBRangeDelTest_TailingIteratorRangeTombstoneUnsupported_Test::TestBody()
    #18 rocksdb/db_range_del_test.cc:1006        main

Address 0x7fc50ae9b868 is located in stack of thread T0 at offset 104 in frame
     #0 librocksdb_src_rocksdb_lib.so+0x13825af  rocksdb::ForwardIterator::RebuildIterators(bool)

[facebook-github-bot]

@ajkr has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[miasantreble]

LGTM, please verify ASAN test passes locally before merging. Thanks

[miasantreble]

block test is failing on phabricator, how about re-run?

[facebook-github-bot]

@ajkr is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[ajkr]

Yes, I verified ASAN passes after the change.