fix(itip): don't parse master as a date when it's missing from the new event

[SebastianKrupinski]

Summary

Broker::parseEvent() throws InvalidDataException: The supplied iCalendar datetime value is incorrect: master when an attendee updates an event and the new version no longer contains the master event the attendee was part of.

Issue

In parseEventForAttendee(), instances are gathered from both the old and new event info. If the old event had the attendee in the master VEVENT, but the new event only contains an instance with a RECURRENCE-ID (some clients, e.g. eM Client with Exchange-originated events, add a RECURRENCE-ID to non-recurring events), the master instance ends up with oldstatus set and newstatus null.

Because the statuses differ, a reply is built for it. Since master is not present in $eventInfo['instances'], the code falls into the branch intended for instances removed via EXDATE and calls DateTimeParser::parse('master', ...), which throws. The exception aborts the whole CalDAV PUT from the client.

Correction

Skip the master instance when generating the reply if the new event has no master instance, since there is nothing to reply for. Replies for the remaining instances (e.g. the one with the RECURRENCE-ID) are generated as before.

{
            "file": "/var/www/nextcloud/3rdparty/sabre/vobject/lib/DateTimeParser.php",
            "line": 205,
            "function": "parseDateTime",
            "class": "Sabre\\VObject\\DateTimeParser",
            "type": "::"
        },
        {
            "file": "/var/www/nextcloud/3rdparty/sabre/vobject/lib/ITip/Broker.php",
            "line": 758,
            "function": "parse",
            "class": "Sabre\\VObject\\DateTimeParser",
            "type": "::"
        },
        {
            "file": "/var/www/nextcloud/3rdparty/sabre/vobject/lib/ITip/Broker.php",
            "line": 253,
            "function": "parseEventForAttendee",
            "class": "Sabre\\VObject\\ITip\\Broker",
            "type": "->"
        },
        {
            "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php",
            "line": 616,
            "function": "parseEvent",
            "class": "Sabre\\VObject\\ITip\\Broker",
            "type": "->"
        },

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.66%. Comparing base (6eee31d) to head (2e9581e).
⚠️ Report is 82 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #794      +/-   ##
============================================
- Coverage     98.76%   98.66%   -0.11%     
+ Complexity     1876     1759     -117     
============================================
  Files            71       71              
  Lines          5345     5167     -178     
============================================
- Hits           5279     5098     -181     
- Misses           66       69       +3     

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