Properly handle invalid dates during recurrence.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13176 e27351fd-9f3e-4f54-a53b-843176b1656c
Properly handle invalid dates during recurrence.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13177 e27351fd-9f3e-4f54-a53b-843176b1656c