What a horrible fix

setKeyguardFadingAway will only be called again with false when
the scrim animation is over. This means that if AM takes to long
to start the animation, something else might have already tried
to fade out the scrim because the device woke up or changed state.

Change-Id: I46f87a4e72f8a8408365c2852df9d2c58d53fd9a
Fixes: 115332000
Test: unlock with PIP and breakpoints