plugins.streamme: Fixed null error for 'origin'
plugins.streamme: Fixed null error for 'origin'

https://github.com/streamlink/streamlink/pull/2307#issuecomment-462113332

```
error: Unable to validate response text: Unable to validate key 'formats': Unable to validate key 'mp4-hls':
Unable to validate key 'origin': Type of None should be 'dict' but is 'NoneType'
```

bastimeyer/streamlink,beardypig/streamlink,chhe/streamlink,gravyboat/streamlink,melmorabity/streamlink,wlerin/streamlink,wlerin/streamlink,bastimeyer/streamlink,melmorabity/streamlink,gravyboat/streamlink,streamlink/streamlink,chhe/streamlink,streamlink/streamlink,beardypig/streamlink