Do not prepare animation if no corresponding animator registered.

If there is no animator can play the corresponding animation, then core
does need to prepare the animation at all.

Flag: EXEMPT bugfix
Bug: 363922376
Test: set default home to 3rd-party launcher, launch app then trigger
back gesture.

Change-Id: I7312cb2795bae47d8920c1e9937bb61cd83f2c11