framework:Thread synchronization for UI update

Issue : Framework reboot was observed due to out of sync between
        two threads which inturn causes Null pointer exception
        while updating airplanemode.
Fix : Handled Null pointer exception and the crash is not observed.
CRs-Fixed: 570122

Change-Id: I2e969f6e7726ffcf8648b366ebb54cb2b0afc292

Conflicts:
	policy/src/com/android/internal/policy/impl/GlobalActions.java