Fixed incorrect handling of mumble:// links

I have fixed a couple of issues in the handling of mumble:// protocol links (detailed in #1190):

- If a user is connected **and authenticated** on a server, and he/she clicks a mumble:// link that connects him/her to the current server, he/she is moved to the channel specified in the link. Previously, this would disconnect and reconnect the user to the server.
- If a user is connected to one server and follows a mumble:// link to another server, he/she is now placed in the channel specified in the link. Previously, the channel they would be moved into would be the channel they were in on the first server.