Matrix rooms remain invite-only forever if they are empty of Matrix users

[progval]

Describe the bug
When there is no Matrix puppet in an IRC channel to writness modes -k or -i being set and there is no privileged Matrix user in the room, then the room is stuck being invite-only

To Reproduce

Steps to reproduce the behavior:

As a channel op:

1. Have at least one Matrix puppet in your channel
2. Set mode +i or +k (this sets the Matrix room to invite-only)
3. Kick all Matrix puppets
4. Unset modes +i/+k

Then the Matrix room can never be joined again

Expected behavior
If every Matrix user leaves (or is kicked from) an invite-only room, then delete/tombstone the room. When another Matrix user tries to join again, apply the normal procedure of trying to join the channel and create a new room

[progval]

Actually, you can join the room with the appservice bot's !join command. thx to @morguldir for pointing it out