camera-menu: Show the menu only if there is more than one camera
camera-menu: Show the menu only if there is more than one camera

Fixes: https://bugzilla.gnome.org/687449

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