[4.0] FieldsHelper: Choose a first available category correctly

[Fedik]

Try to fix release blocker #23036 .

Summary of Changes

This is correcting a way to retrieve a first category in list

Testing Instructions

Apply patch, and create a field assigned to specific category.
Then create a new Article to this category and make sure the field is there.

Actual result BEFORE applying this Pull Request

Works

Expected result AFTER applying this Pull Request

Works

Documentation Changes Required

nope

ping @wilsonge

[SharkyKZ]

I have tested this item ✅ successfully on a5eef98

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[ceford]

I have tested this item ✅ successfully on a5eef98

If it works before and works after applying the patch it is not clear what to look for as a test result.

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[Quy]

RTC

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[wilsonge]

Do we need this same code in the other places we have this (WorkflowBehaviorTrait and ArticleModel)?

[Fedik]

Good question, I did not seen it there,
if it use

$xml->loadHTML($formField->__get('input'));
$options = $xml->getElementsByTagName('option');

Then yes, it also need to be changed.

Do not merge it for now, I will check that also

[Fedik]

I have updated WorkflowBehaviorTrait and ArticleModel. Please re-check

I just have no idea where to test WorkflowBehaviorTrait.

[Fedik]

@Quy please restore an yellow label 😉

[dgrammatiko]

I have tested this item ✅ successfully on 861f892

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[wilsonge]

Thanks!

[wilsonge]

(Merged as there was two good changes in the main patch and one good test on rolling the same thing out to two other places)