#825 Client disappear from roster after leaving the session

[AndrejSz]

The host couldn't see the client in his contact list, after the client leaves the session.

Test Case:
Alice invites Bob in a session and he accepts.
Bob leaves the session.
Alice let the running session open but she is alone in the session.
Alice don’t see bob in her contact list until she leaves the session.

[Stefan Rossbach]

c5f384d717decd54b67bdbca3c66d1ac5807d845