Fix today marker in Months screen sometimes disappearing.

To reproduce: with stale Months screen, make app
inactive, then active again.
Add launch screen as xib and remove asset catalog entry.
Minor configuration cleanup.
Prevent crashing when dismissing to Day screen.

This happens when date gets edited on Events
screen for the last event on that day.
Prevent crashing when dismissing to Months screen.

This happens when the day no longer has any
events due to editing.