Fix NPE when animation doesn't get started

If animation start is delayed, there is no guarantee that
startAnimation is called on the adapter. Thus, protect
RemoteAnimationController against this case, as leash and
finishedCallback would be null.

Furthermore don't even try to start remote animation that is
delayed as it would leave it hanging forever.

Test: SurfaceAnimatorTest/RemoteAnimationControllerTest
Change-Id: I72c492c4fb6ca8eeae481d2c281e9c1fee95f921
Fixes: 76096628