Don't print Sending EDU if there is noone to send to (#721)
Don't print Sending EDU if there is noone to send to (#721)

The logs had a lot of:

```
Sending EDU event                             destinations="[]" edu_type=m.typing
```

Which is useless if it isn't actually sending the event anywhere (destinations is empty).
matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite