Add error handling to prevent IllegalArgumentException

ActivityLaunchAnimator.Controller.fromView requires an instance of LaunchableView, however findViewWithBackground had no checks to return one. updated the check to make the exception less likely.

Flag: not needed
Fixes: 297564681
Test: ran launcher and launched apps
Change-Id: Iddbe55c1ff66b067f8456d058cbc60a2a698c4ae