Add fallback to reset the waiting for transition state.

- When launching into recents directly in another orientation, it
  appears that the animation start callback is not made, which then
  causes the transition-waiting state to persist until Overview is
  next hidden. As a fallback, if we get onEnterAnimationComplete()
  on the activity, then the animation has started and completed, so
  we can reset the state.

Bug: 64694148
Test: Launch fixed-portrait app, hold device in landscape and then hit
      recents button, ensure that recents button still works after.

Change-Id: Ibac8554c1f71324838fef1f04db2d88b16ffe219