Make dismiss layout invisible rather than gone

Test: manual 1) have a stack of bubbles, fling to dismiss them
             2) add another bubble
             3) expand the stack
             4) tap on the bubble while stack is expanded => it shouldn't
                fly off the top of the screen
Fixes: 138445026
Change-Id: If09ba2a9f4ce4e5a5441ebea7c2801a68dfe3d59