Files section: fix NaN after file sort

[distantnative]

This PR …

https://github.com/getkirby/kirby/blob/main/panel/src/panel/upload.js#L293

When there is no template and not sortable, attributes is actually empty (see https://github.com/getkirby/kirby/blob/main/config/sections/files.php#L194-L200). In turn, attributes is not an empty object but actually ends up as an empty array in JS world. And .sort on an array is a method, which is why the if statement gets entered and then NaN is the result.

Fixes

• Files section: fixed NaN value after sorting files
  Files section sort value NaN #6067

Ready?

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

For review team

• Add changes to release notes draft in Notion
• Add to website docs release checklist (if needed)

[bastianallgeier]

Couldn't this be in 4.0.4?

[distantnative]

For my taste it's not enough in the "this will 100% cause no issues" category