Fix memory overlap in MOT checkpoint SerializeInProcessTxns

src/gausskernel/storage/mot/core/src/system/checkpoint/checkpoint_manager.cpp

@@ -927,10 +927,10 @@ bool CheckpointManager::SerializeInProcessTxns(int fd)
                 return RC_ERROR;
             }
             MOT_LOG_DEBUG("SerializeInProcessTxns: wrote seg %p %lu bytes", segment, bufSize);
+        }
         if (buf != nullptr) {
             free(buf);
         }
-        }
         return RC_OK;
     };