dig warning as output when no response

When there is no response for a specific record type, but there is a warning from dig, the warning is returned as output.

Observed output:

```
>>> pydig.query("*.XXXXXX.com", "A")
[';; Warning: Message parser reports malformed message packet.']
```

Expected output:
```
>>> pydig.query("*.XXXXXX.com", "A")
[]
```
