Fix NPE if animation updated after manager released.

NPE occurs when onAnimationUpdate is called after
BackgroundManager has been released.
Cancel animation on BackgroundManager released.

Test: run support-leanback-demo
Bug: https://code.google.com/p/android/issues/detail?id=233511
Change-Id: I574747493a4f9d7ee1544190c30d2e1ed248b480
(cherry picked from commit 92d8453dfc8ee5153e5d207618c4555d0a14e8f7)
1 file changed