Fix PartialWakeLock regression

Removed mAnimating due to it always being false, but accidentally
read a condition backwards and removed a line instead of making
it always run. This line caused WindowAnimator to run continuously
even when there was nothing to animate

Bug: 150486411
Test: PowerTest#power2PartialWakeLockCheckTest passes again
Change-Id: Ia0ab48103d4c34edbac1ad08b3aab1b5723db2ea