DAV resource: support exception incidences
My calendar has a few events like [...] BEGIN:VEVENT # the only one DTSTAMP:20210510T164410Z CREATED:20210510T164409Z LAST-MODIFIED:20210510T164410Z DTSTART;TZID=Europe/Paris:20210511T143000 DTEND;TZID=Europe/Paris:20210511T153000 RECURRENCE-ID;TZID=Europe/Paris:20210513T143000 [...] They show up in roundcube but were missing in korganizer. I'm no ICAL expert but I think those are exceptions to a recurring event, detached from that recurring event. And indeed after this fix, they show up as "Recurrence: Exception" in korganizer. Found by debugging "Failed to parse item data" warnings from the DAV resource.