remove privacy list from dialog only when server return the result, else show an error dialog. fixes #2853

simon, could you have a look to this patch ? does it seems correct ?

(Open gc win three times faster, and even more when time cached !
Also opens history wins two times faster)

(stop drawing it 5 times when joining muc, stop reloading banner state icon on ALL
notifications, ...)
roster.py one seems useless because ctrl.update_ui() did it already

Catch only what you expect. We don't want to catch things like unknown variables (and other programming errors) and SystemExit.