save ddl ret_code when switch_status

src/rootserver/ddl_task/ob_index_build_task.cpp

@@ -349,6 +349,7 @@ int ObIndexBuildTask::init(const ObDDLTaskRecord &task_record)
     }
     task_id_ = task_record.task_id_;
     parent_task_id_ = task_record.parent_task_id_;
+    ret_code_ = task_record.ret_code_;
     is_inited_ = true;
   }
   return ret;