Defer cleaning up screenshot until after we actually switch to screenshot

- In the case where we get a screenshot on cancel, we should wait to
  finish the recents animation until the view gets a chance to update

Bug: 185643608
Test: Swipe up to overview in 2 button, hit home
Change-Id: I2ac3567006f6fa7e6f473499f6862e5e408dfc3d