Bug 452656

SUMMARY
It would appear that in some cases, the information provided to the calDAV server is invalid, causing it to be rejected.

Specifically, `VTIMEZONE` components missing a required `STANDARD` or `DAYLIGHT` component as noted in RFC5545 (a VTIMEZONE component MUST contain at least one `standardc (STANDARD)` or `daylightc (DAYLIGHT)` component -- https://datatracker.ietf.org/doc/html/rfc5545#section-3.6.5 )


STEPS TO REPRODUCE
1. Start to create a new event on a calendar hosted on a radicale (I'd assume others but havent tested)
2. Set the timezone to Africa/Johannesburg (this is my local timezone -- Obvserved issue with `UTC-10` as well)
3. Save the event

OBSERVED RESULT
```
BEGIN:VCALENDAR
PRODID:-//K Desktop Environment//NONSGML libkcal 4.3//EN
VERSION:2.0
X-KDE-ICAL-IMPLEMENTATION-VERSION:1.0
BEGIN:VTIMEZONE
TZID:Africa/Johannesburg
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20220415T111224Z
CREATED:20220415T111224Z
UID:84632fb4-6e5e-40ed-9d05-c8192822574a
LAST-MODIFIED:20220415T111224Z
SUMMARY:test four
DTSTART;TZID=Africa/Johannesburg:20220417T131500
DTEND;TZID=Africa/Johannesburg:20220417T141500
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR
```

Is sent to the calDAV server, note the invalid VTIMEZONE of:
```
BEGIN:VTIMEZONE
TZID:Africa/Johannesburg
END:VTIMEZONE
```
Where it should include a STANDARD clause indicating its offset

All this ends with is radicale rejecting the invalid event, and thus it not being propagated to things

EXPECTED RESULT
Event is correctly sent to my calDAC server