Fix windows leaked in ZenModeScheduleRuleSettings

ZenModeScheduleRuleSettings creates an DaysDialog when user clicked
Days option.

If Activity was destroyed suddenly, WindowsManager throws a windows leaked exception.
And then DaysDialog try to do something(dismiss), settings app will crash.

So, we need to dismiss dialog when activity was destroyed.

Test: robo test, change code to recover symptom, manual test
Change-Id: I8d5370fe9673573581d613da91c7ab9be55d8199
Fixes: 111841375