Closes#13847.
I think we can probably get some test coverage of this if required, but
needs a bit of thought (basically an error needs to be thrown during the
multiplayer client portion of the join procedure, after `CurrentRoom` is
non-null but before the join completes).
Manual testing on password branch (#13861) is possible since it
currently errors due to missing method on the live/dev servers.
- Create game, which will fail with `MethodNotExists`.
- Note the fields on the settings screen are emptied.
- Fill fields again and press create game (crash).