Prevent NPE in not attached Clock

If we receive a broadcast in a not attached Clock (as the receiver
Handler is not the main Handler), do not post messages if we do not have
a UI handler.

Test: manual, wait until time change
Test: manual, change locale and timezone
Fixes: 144296310
Change-Id: Ie8a2627004876cf35291d52bd3686a5014498f52
1 file changed