Fix KeyError bug

[MutedByte]

Traceback (most recent call last):
  File "C:\Program Files\Python310\lib\site-packages\revolt\websocket.py", line 92, in handle_event
    await func(payload)
  File "C:\Program Files\Python310\lib\site-packages\revolt\websocket.py", line 131, in handle_messageupdate
    if data["content"]:
KeyError: 'content'

fix
raises when message doesn't have content

[Zomatree]

This doesnt fully fix the issue, this has been fixed already.