dav: Fix fatal error when ORGANIZER is missing in CalDAV schedule

[AlessioDiPretoroAsdea]

• Resolves: [Bug]: Fatal Error in CalDAV Schedule Plugin: Call to a member function getNormalizedValue() on null #59266

Summary

This PR fixes a Fatal Error: Call to a member function getNormalizedValue() on null in the CalDAV Schedule Plugin.

The error occurs when an event (e.g., synchronized from external sources like Google Calendar) does not contain an ORGANIZER property. Using the PHP 8 null-safe operator ensures the synchronization doesn't crash with a 500 error.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits (DCO)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[tcitworld]

Fix looks good enough, I just wonder if there's a way that $adresses could contain the null value. In that case we better check that $vevent->ORGANIZER?->getNormalizedValue() isn't null outside the  in_array condition first.

[AlessioDiPretoroAsdea]

Thanks for the review!

I encountered this bug while syncing Google Calendar events to Nextcloud using vdirsyncer. Some events from Google don't seem to have a technical 'Organizer' field, which leads to the fatal error.

Since I'm not a PHP expert, I'm not sure if $addresses could ever contain a null value in this context. If you think an explicit check for null is safer, please let me know and I'll try to update the code accordingly!

[kesselb]

Block unconventional commits / Block unconventional commits

To resolve please change the ocmmit message like

fix(dav): Avoid fatal error for events without an organizer

(the current message fails, because "dav" isn't valid. It must be either fix, feat, refactor, chore, test, ci).

[AlessioDiPretoroAsdea]

@kesselb @tcitworld
Thanks for the feedback! I've updated the code using isset() and fixed the commit message format to follow the conventional commits standard. Re-pushed now.

[kesselb]

/backport to stable33

[kesselb]

/backport to stable32

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