fix memory leak in db_stress checkpoint test (#7813)

Summary:
fix memory leak in db_stress checkpoint test. If s is not ok, checkpoint is not deleted, may cause memory leak.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7813

Test Plan: make asan_check

Reviewed By: cheng-chang

Differential Revision: D25702999

Pulled By: zhichao-cao

fbshipit-source-id: 08253b0852835acb8cfd412503cdabf720afb678

db_stress_tool/db_stress_test_base.cc

@@ -1505,11 +1505,11 @@ Status StressTest::TestCheckpoint(ThreadState* thread,
       }
     }
   }
+  delete checkpoint;
+  checkpoint = nullptr;
   std::vector<ColumnFamilyHandle*> cf_handles;
   DB* checkpoint_db = nullptr;
   if (s.ok()) {
-    delete checkpoint;
-    checkpoint = nullptr;
     Options options(options_);
     options.listeners.clear();
     std::vector<ColumnFamilyDescriptor> cf_descs;