Don't block TIME_TICK broadcasts in the DigitalClock widget.

This change applies the fix -- originally by phanna in
https://android-git.corp.google.com/g/#change,33669 -- to
the com.android.internal.widget version of DigitalClock,
which is used by the keyguard and pattern lock screens.

Change-Id: I43f72dd144423e55f73ba52903d52163c8f65591