end() a reverse()'d animation correctly

Previously, an animator that had been reverse()'d (and was thus
playing backwards) would not end() at the right value. That is, a call
to end() would cause the animation to snap to its original end value, not
the reverse-playing end value (i.e., its start value). Logic to handle
calculating the proper end value was not taking the reversing behavior
into account.

Issue #6583656 When you call end() after calling reverse() on an animation that has not started leads to forward animation finishing.

Change-Id: Ifca60a32d4973c21b85aed9c459f802526c0207e