Update searches.php: Fixing panel search when uuids are disabled

[toebu]

This PR fixes a bug that would break the panel search when uuids are disabled

I couldn't find an open issue about this (which surprised me quite a bit). If UUIDs are disabled, the panel search is completely broken since 4.0. This is a quick fix that I think fixes this, but this is my first time contributing to Kirby, so I'm not too sure...

Explanation of the fix: $page->uuid() returns null when uuids are disabled. Calling toString() on null throws an exception. With the fix, toString() is not called and null is used instead.

Fixes

• Panel search fixed when UUIDs are disabled

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and checks all pass

For review team

• Add lab and/or sandbox examples (wherever helpful)
• Add changes & docs to release notes draft in Notion

[bastianallgeier]

Thanks for this fix!

[toebu]

Awesome, thanks for merging so quickly!