Ensure the above-top finishing activity is invisible

The finishing activity was the top-most activity in the Task. The
activity was not updated to invisible because it was above the
top running activity.

Bug: 259566326
Test: Starts a fullscreen activity in a new Task on top that
      resulted in two activities below (in ActivityEmbedding)
      to pause while the pausing activity is also finishing
Change-Id: I446cadf84afd4cad54f357fe9fec5ec6e8ac47b8