power: Don't forget about disabled touchscreens

When blanking the screen twice, which can happen when suspending,
don't forget about previously disabled touchscreens.

See https://bugzilla.redhat.com/show_bug.cgi?id=1173849

https://bugzilla.gnome.org/show_bug.cgi?id=743252

Conflicts:
	plugins/power/gsd-power-manager.c