Ensure animator's interpolator is set

Animator's play state can go from NotStarted to Finished directly
in the case of calling start() and end() within one frame. Previously
we only set animator's interpolator when the animator is transitioning
to Running state. So when Running state is skipped, the interpolator
is left unset.

Bug: 27224373
Change-Id: I5a53106fe1aae38ccaf1df8debd553be3bc56133