Fix minimized dock

- When SysUI crashed, make sure state is up-to-date
- When divider gets invisible, update state because animations
won't finish
- Make sure to keep mMinimizedDock up-to-date in all cases, even
if docked stack is already gone.
- If docked stack is going away, reset minimized state
- Disallow undocking when minimized.

Bug: 27588187
Bug: 27486464
Change-Id: I6ea48562fae3a8df038a690a488580d758681370