Skip marking recents as pending top if it is already on top

Otherwise when cleaning up recents animation without further
transition, the fixed rotation state is not cleared.

Since live tile is enabled, when using home key (button navigation
mode) to leave overview, the recents animation will be finished
after starting home, so home is already on top. Then the method
notifyRecentsWillBeTop that used for deferring clear fixed rotation
until next transition should not be called.

Fixes: 193032496
Test: RecentsAnimationControllerTest
Change-Id: Icbe27f6b3d84c948a75d6dabebab1f6b469bbc4d