Describe the bug When you receive a private message from within a MUC a new chat with the address of the MUC is created, e.g. ejabberd-de@conference.conversations.im. Trying to join that MUC is crashing SiskinIM.

To Reproduce Steps to reproduce the behavior:

• have a private message from a MUC you haven't currently joined in SiskinIM, e.g. by asking someone to send you a private message in that MUC.
• this should open a new chat in Siskin with address of the MUC
• now try to join the MUC by tapping on the "+" and "Join group chat" and enter the appropriate settings.
• when tapping on Join, Siskin crashes.

Expected behavior Well, not crashing of course... ;-) Maybe check against addresses of existing chats and act accordingly...