Initialize options.row_cache

Summary: options.row_cache should already been initialized as null by default. Still try to set it following current convention, because one valgrind failure reports a failure related to it.

Test Plan: Run all unit tests

Reviewers: yhchiang, kradhakrishnan, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D51303

util/options.cc

@@ -260,6 +260,7 @@ DBOptions::DBOptions()
       delayed_write_rate(1024U * 1024U),
       skip_stats_update_on_db_open(false),
       wal_recovery_mode(WALRecoveryMode::kTolerateCorruptedTailRecords),
+      row_cache(nullptr),
 #ifndef ROCKSDB_LITE
       wal_filter(nullptr),
 #endif  // ROCKSDB_LITE