Reapply fix for #13166 (#13265)

Summary:
There was a fix in #13171 for issue #13166 but it was overwritten by commit d5345a8. This PR is to reapply the fix.

Fixes #13264 to have Rocks compile under Ubuntu again

Pull Request resolved: #13265

Reviewed By: archang19

Differential Revision: D67764706

Pulled By: cbi42

fbshipit-source-id: c8822fff6769bf3be1e6ceee3f2b58b09d8569b3

memtable/wbwi_memtable.h

@@ -367,7 +367,7 @@ class WBWIMemTableIterator final : public InternalIterator {
       key_.clear();
       valid_ = false;
       s_ = Status::Corruption("Unexpected write_batch_with_index entry type " +
-                              std::to_string(t->second));
+                              std::to_string(it_->Entry().type));
       return;
     }
     key_buf_.SetInternalKey(it_->Entry().key, assigned_seqno_.upper_bound,