Pull Request for Issue #17305

As info: I have written a plugin that adds JPagination navigation and an extended toc for specific articles in a similiar way like plg_content_pagebreak does but that listens to another tag/regex. Whenever there is no "system-pagebreak" marker inside an article plg_content_pagebreak throws a 404 then.

Summary of Changes

• Remove exception that ignores that several use cases and extensions could use pagination or toc without "system-pagebreak" regexes. The exception was added with #11217
• Set "Simple performance check" earlier.

Testing Instructions

• See #17305 for cases where the exception creates annoying conflicts.
• Apply patch and test again if any failures come up.

Expected result

• Also other extensions can use JPagination and things similiar like TOC (start=xyz) without failures.
• It should be possible to use these extensions without deactivating plg_content_pagebreak that could be used in other articles.
• Even if placed lately in code lines https://github.com/joomla/joomla-cms/blob/staging/plugins/content/pagebreak/pagebreak.php#L132-L135 should be sufficient as "page-exists?-test"

Actual result

• One have to deactivate plg_content_pagebreak to get no 404 or have to kick custom extensions that use Joomla features and standards (e.g. $page that comes from core).
• The only way to get rid of this 404 is to add a senseless class="system-pagebreak to your custom extension tag or the article text before plg_content_pagebreak works. Bad practice. [EDIT: That's a stupid idea because plg_content_pagebreak then throws another exception. I don't understand at all why this plugin has to throw 404 exceptions.]