Summary:
We may sometimes read the uncompression dictionary when its not
necessary, when we lookup a key in an SST file but the index indicates
the key is not present. This can happen with index_type 3.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6906
Test Plan: make check
Reviewed By: cheng-chang
Differential Revision: D21828944
Pulled By: anand1976
fbshipit-source-id: 7aef4f0a39548d0874eafefd2687006d2652f9bb