OMEMO: doesn't work in MUCs if there is only one participant
Steps to reproduce
Create private, non-anonymous MUC room
Make sure you're the only one in it
Enable OMEMO encryption
Try to send the message
Message has been sent and is visible on all devices.
"To send an encrypted message, you have to first trust the fingerprint of your contact!" green error text appears.
But I'm already trusting all of my devices!
I think this is caused by my MUC room having only one participant - me.
For the record, a similar issue exists in Conversations: https://github.com/siacs/Conversations/issues/2768