Re-evaluate scrim color on keyguard vis event

The color of the scrims depends on the keyguard visibility.
This CL fixes a race condition where the keyguard state would be
delayed causing the scrim color to be wrong.

Test: unlock device with fp multiple times (unlock to activity)
Fixes: 110994792
Change-Id: I4715159b961fa7c989bfdca9088229bff40054aa