Settings: Don't crash if we pause too quickly

Notifier is unregistered in every case in pause.
However, if you close the Settings app too quick, the notifier
might not be registered at all, causing an IllegalArgumentException
during the unregistering.

Conflicts:
	src/com/android/settings/Settings.java

Change-Id: I9cd8934c3dd208cc6d78143de5d1457995e06c5c