Sometimes Android events don't have DTEND/DURATION, although it's required by...

Sometimes Android events don't have DTEND/DURATION, although it's required by Android calendar provider.
In this case, assume 1 hour (non-all-day events) or 1 day (all-day events) because many servers don't
understand events without DTEND. So VEVENTs without DTEND should only be generated
when explicitly required by dtStart=dtEnd in the Android event.