Allow infinite-repeat zero-duration animators to continue repeating

A recent change to ValueAnimator caused infinitely repeating animators with
duration 0 to be ended immediately. BatterySaver mode can cause animators
to have 0 duration, which means that apps depending on animator update events
no longer receive those events due to this behavior change.

The fix is to restore the previous behavior of allowing repeating animators
to continue, regardless of duration.

Issue #19113776 Fix infinite-repeating, zero-duration animator behavior

Change-Id: I4d1c7afb6d06ca45ef41db73c160f6a6d5754e24