logind: when setting a new controller, don't prepare the VT if logind is restarted

logind: when setting a new controller, don't prepare the VT if logind is restarted

When assigning a new session controller to a session, the VT is prepared so the
controller can expect the VT to be in a good default state.

However when logind is restarted and a session controller already took control
of a session, there's no need to prepare th VT otherwise logind may screw up
the VT state set by the controller.

This patch prevents the preparation of the VT in this case.