[4.3] Prevent modal from closing when showing an error

[heelc29]

Pull Request for Issue #39150 .

Summary of Changes

The modal is only closed if the iframe does not contain an element joomla-alert[type="danger"].

Testing Instructions

see #39150

The error also occurs with Single Contact (if name contains only spaces):

Actual result BEFORE applying this Pull Request

Modal is closed

Expected result AFTER applying this Pull Request

Modal still open and show error message (like when only Save is clicked)

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[alikon]

@heelc29 can you please contact me vicepresident.at.opensourcematters.org

[HLeithner]

This pull request has been automatically rebased to 4.3-dev.

[chmst]

I have tested this item ✅ successfully on bc5f9c3

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[fancyFranci]

I have tested this item ✅ successfully on bc5f9c3

I tested the case from the issue and the PR does not let the modal close.

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[richard67]

RTC

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[obuisard]

Thank you @heelc29 for this PR