DeskClock: Stop editing time when pausing the app

* Currently adding a new alarm, pausing the app and then resuming it
  can lead to an existing alarm being changed
* Instead of relying on stored values or the user even remembering which
  alarm he edited (or wanted to add) last, close the picker

Reproduction:
- Expand an alarm
- Press FAB
- Lock device and unlock again
- Press OK in the picker - last expanded alarm is edited instead of
  a new one being created

Fixes: https://gitlab.com/LineageOS/issues/android/-/issues/5035
Change-Id: Id38071a5726227cc91d881de18551b956cef3328