Fix: Fix Admin Settings page when Watermark label selected

[Koc]

• Target version: main

Summary

Reproducer:

1. Open settings
2. Enable watermark that will apply on files with some tags
3. Refresh page

Expected result:
It is possible view and change tag that used for watermark assigning.

Actual result:
There is an error Error in render: "TypeError: option is undefined".

TODO

• Backport to stable 29

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Documentation (manuals or wiki) has been updated or is not required

[elzody]

Looks okay, only one suggestion

[elzody]

/backport to stable30

[elzody]

/backport to stable29

[elzody]

The failing tests are unrelated, looks good to me. Could not reproduce the original issue on stable28, so only backporting to stable29.

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