message: fix onTask crash.
diff: @@ -163,6 +163,12 @@ int swTaskWorker_finish(swServer *serv, char *data, int data_len, int flags)
  uint16_t source_worker_id = current_task->info.from_id;
  swWorker *worker = swServer_get_worker(serv, source_worker_id);
  + if (worker == NULL)
  + {
  + swWarn("invalid worker_id[%d].", source_worker_id);
  + return SW_ERR;
  + }
  +
  int ret;
  //for swoole_server_task
  if (swTask_type(current_task) & SW_TASK_NONBLOCK)
  