Fix selection after dismissal

When dismissing a bubble, mIsBubbleSwitchingAnimating should only be
true if it's the current bubble being dismissed. If a different
bubble is selected, then no switching animation will need to be
run.

Bug: 234621652
Bug: 234069335
Test: manual - have multiple bubbles, expand the stack, dismiss
               a bubble that isn't currently selected
               => verify that you can select a different bubble after
               dismissing
Change-Id: Ice4ade66d49e1bd302defab142ae367c4a889cfd