Fix the potential memory leak of ReplayMultiThread (#5949)

Summary:
The pointer ra needs to be freed the status s returns not OK. In the previous  PR https://github.com/facebook/rocksdb/issues/5934  , the ra is not freed which might cause potential memory leak. Fix this issue by moving the clarification of ra inside the while loop and freeing it as desired.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5949

Test Plan: pass make asan check.

Differential Revision: D18045726

Pulled By: zhichao-cao

fbshipit-source-id: d5445b7b832c8bb1dafe008bafea7bfe9eb0b1ce

trace_replay/trace_replay.cc

@@ -313,13 +313,13 @@ Status Replayer::MultiThreadReplay(uint32_t threads_num) {
       std::chrono::system_clock::now();
   WriteOptions woptions;
   ReadOptions roptions;
-  ReplayerWorkerArg* ra;
   uint64_t ops = 0;
   while (s.ok()) {
-    ra = new ReplayerWorkerArg;
+    ReplayerWorkerArg* ra = new ReplayerWorkerArg;
     ra->db = db_;
     s = ReadTrace(&(ra->trace_entry));
     if (!s.ok()) {
+      delete ra;
       break;
     }
     ra->woptions = woptions;