presence-chooser: only listen to EmpathyIdle::notify::state
presence-chooser: only listen to EmpathyIdle::notify::state

Previously, when the global presence changed in EmpathyIdle, it would
notify for "state" and "status", so the state change callback would be
called twice.

Signed-off-by: Jonny Lamb <3d1fb3642aaab2ff70e3392a5ab916bf99eed6a3@collabora.co.uk>

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