keyguard: enable magnetic target if no custom targets defined

When no custom target is defined (the "reset" button is pressed
in settings), the unlock target will always be at the right
regardless of the direction the user dragged to.

Change-Id: I0a2b1cd5dc7a2840c23d83a26593513cbc880c08

Conflicts:
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardSelectorView.java