list_dispatch return 503 if room not exists

```python
await lk_api.agent_dispatch.list_dispatch('a')
```
```bash
livekit.api.twirp_client.TwirpError: TwirpError(code=unavailable, message=twirp error unknown: no response from servers, status=503)
```

maybe something else other than 503, like 404, or just empty