add missing check for hash index when calling BlockBasedTableIterator (#5712)

Summary:
Previous PR https://github.com/facebook/rocksdb/pull/3601 added support for making prefix_extractor dynamically mutable. However, there was a missing check for hash index when creating new BlockBasedTableIterator. While the check may be redundant because no other types of IndexReader makes uses of the flag, it is less error-prone to add the missing check so that future index reader implementation will not worry about violating the contract.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5712

Differential Revision: D16842052

Pulled By: miasantreble

fbshipit-source-id: aef11c0ff7a690ed248f5b8fe23481cac486b381

table/block_based/block_based_table_reader.cc

@@ -3084,7 +3084,8 @@ InternalIterator* BlockBasedTable::NewIterator(
         arena->AllocateAligned(sizeof(BlockBasedTableIterator<DataBlockIter>));
     return new (mem) BlockBasedTableIterator<DataBlockIter>(
         this, read_options, rep_->internal_comparator,
-        NewIndexIterator(read_options, need_upper_bound_check,
+        NewIndexIterator(read_options, need_upper_bound_check &&
+                         rep_->index_type == BlockBasedTableOptions::kHashSearch,
                          /*input_iter=*/nullptr, /*get_context=*/nullptr,
                          &lookup_context),
         !skip_filters && !read_options.total_order_seek &&