[4.1] Prevent deleting a parent template if children exist

[dgrammatiko]

Pull Request for Issue # .

Summary of Changes

To prevent possible disaster (deleting a parent template but child still around and default) a simple check was added in the installer

Testing Instructions

• Install https://github.com/joomla/joomla-cms/files/7235154/cassy_1.0.0.zip
• Create a child template
• try to uninstall Cassy

Actual result BEFORE applying this Pull Request

The parent template will be removed

Expected result AFTER applying this Pull Request

Error message and parent template wasn't removed

Documentation Changes Required

[khu5h1]

I have tested this item ✅ successfully on de5b4ff

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[RickR2H]

I have tested this item ✅ successfully on de5b4ff

Patch works! @dgrammatiko Not related but probably good to mention. I noticed that the icons of the Cassy theme are missing. Also the CSS custom properties of the template styling are missing. Switching to Cassy theme will leave the header transparent.

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/36191.}

[RickR2H]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/36191.}

[dgrammatiko]

Also the CSS custom properties of the template styling are missing. Switching to Cassy theme will leave the header transparent.

Yes, you're right the template was created for another PR (the wysiwyg tinyMCE) and I haven't updated it since. Probably I will since I want a base template with dark support...

[bembelimen]

Thx