Minor fix: single delete a blob value is not a mismatch (#4848)

Summary:
In compaction iterator, if the next value of single delete is a blob value, it should not treated as mismatch. This is only a minor fix and doesn't affect correctness.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4848

Differential Revision: D13585812

Pulled By: yiwu-arbug

fbshipit-source-id: 0ff6223fa03a644ac9fd8a2d77f9d6711d0a62b0

db/compaction_iterator.cc

@@ -407,7 +407,8 @@ void CompactionIterator::NextFromInput() {
             // is an unexpected Merge or Delete.  We will compact it out
             // either way. We will maintain counts of how many mismatches
             // happened
-            if (next_ikey.type != kTypeValue) {
+            if (next_ikey.type != kTypeValue &&
+                next_ikey.type != kTypeBlobIndex) {
               ++iter_stats_.num_single_del_mismatch;
             }