Fix compatibility break in validation.js

[Fedik]

Summary of Changes

As result of #39350 it become impossible to use validation over non <form> element.
Hovewer some extensions use this feature to validate form "per section".

Testing Instructions

Apply patch. Run npm install
Open a form for "New article".
In Browser console, run 2 commands (one by one):

document.formvalidator.isValid(window['item-form']);

document.formvalidator.isValid(window['item-form'].parentElement);

Actual result BEFORE applying this Pull Request

First command executed, and you get a validation message.
Second command throws an error

Expected result AFTER applying this Pull Request

Both commands works, and shows validation message

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[viocassel]

I have tested this item ✅ successfully on 819f565

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/40230.}

[obuisard]

I have tested this item ✅ successfully on 819f565

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/40230.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/40230.}

[obuisard]

Thank you Fedir @Fedik for the fix

[compojoom]

thanks for the fix @Fedik ! Will there be a 4.2.10 release with this fix?

[obuisard]

thanks for the fix @Fedik ! Will there be a 4.2.10 release with this fix?

No, you will have to wait for 4.3, coming April, 18 :-)