[4.0] Fix PHP error with pagebreak

[C-Lodder]

Pull Request for Issue #28795

Summary of Changes

Fix a PHP error being throw with the pagebreak plugin

Testing Instructions

1. Add a page break to any article
2. View the article in the frontend

Expected result

The article is displayed

Actual result

PHP error

[alikon]

I have tested this item ✅ successfully on 3a1f061

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[faustonenci]

I have tested this item ✅ successfully on 3a1f061

good

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[alikon]

RTC

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[adj9]

I have tested this item ✅ successfully on 3a1f061

I confirm what happens in the frontEnd with an article that has the page break.
click on bleak and Articol index is moved

Without patch there is the error
The requested page can't be found.

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[richard67]

Thanks all.