Check if running task is null in onPrepareGestureEndAnimation

- The crash happen when swiping to overview from home without any task in recents
- A simple null check fixes the issue

Fix: 194166137
Test: FallbackRecentsTest#goToOverviewFromHome
Change-Id: I9344a96a4a78fcfc88d2ad53e44ecd43b23114d5
1 file changed