message: fix CID#1460221
diff: @@ -611,7 +611,7 @@ static PHP_METHOD(swoole_coroutine_util, sleep)
  context->state = SW_CORO_CONTEXT_RUNNING;
  php_swoole_check_timer(ms);
  - if (SwooleG.timer.add(&SwooleG.timer, ms, 0, context, php_coroutine_sleep_timeout) < 0)
  + if (SwooleG.timer.add(&SwooleG.timer, ms, 0, context, php_coroutine_sleep_timeout) == NULL)
  {
  RETURN_FALSE;
  }
  