_strip_single_event() removed the recurrence-defining properties (RRULE,
EXDATE, EXRULE, RDATE) with a single try/except around sequential
delattr() calls. When one of them was absent (e.g. an event with no
EXDATE), the AttributeError aborted the whole block and the following
properties -- notably RDATE -- were left on the expanded
single-occurrence VEVENTs returned by a calendar-data expand REPORT.
Remove each property independently so a missing one no longer prevents
removal of the others. Add a regression test and fixture.
Co-Authored-By: Claude <noreply@anthropic.com>