message: Fix a null pointer segment fault when call swoole_server::stop in task worker
diff: @@ -4117,8 +4117,11 @@ PHP_METHOD(swoole_server, stop)
  }
  if (worker_id == SwooleWG.id && wait_reactor == 0)
  + {
  + if (SwooleG.main_reactor != NULL)
  {
  SwooleG.main_reactor->running = 0;
  + }
  SwooleG.running = 0;
  }
  else
  