fix(dav): allow multiple organizers if possible

fix(dav): allow multiple organizers if possible

This is very hacky! However, we want to allow saving events with multiple
organizers. Those events are not RFC compliant, but sometimes imported from major
external calendar services (e.g. Google). If the current user is not an organizer of
the event we ignore the exception as no scheduling messages will be sent anyway.

Signed-off-by: Richard Steinmetz <richard@steinmetz.cloud>