SystemUI: bail out of recents-to-home animation when losing focus

In the case when recents is animating out, and an application happens to
immediately add a view to the window manager, the recents view would
lose its focus, but the animations would continue to run, breaking the
behavior in certain cases.

Bail out of the recents activity and override the pending transition to
be disabled to not distrubt the newly added window.

Ref: CYNGNOS-1136

Change-Id: I5998a9dcf21b1369473f04ea4d867c5f2543d6df
Signed-off-by: Roman Birg <roman@cyngn.com>