Fix problem with zero-duration AnimatedVectorDrawables

There was an issue with some vector drawables, particularly those with more
than one underlying, sequential animators, where the final frame would not be
drawn when battery saver mode was enabled (or animators were set to have durations
of 0). This resulted in an incorrect fingerprint graphic on the lockscreen, because
the animation effectively didn't run at all.

The fix is to always invalidate whenever the AnimatedVectorDrawble draws itself. This
causes us to constantly invalidate() the view while the animation is running.

Issue #26591987 Fingerprint icon displayed as dots when batter saver mode is on

Change-Id: I13cbd71fd229db09418c6dcacfec5a13bbb44b2e