roster-view: clear the view when disposing
roster-view: clear the view when disposing

https://bugzilla.gnome.org/show_bug.cgi?id=683699

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets