Fixing broken Folder::exists()

[Hackwar]

Followup Pull Request for pr #40239.

Summary of Changes

Fixes the error message undefined method Folder::exist, which comes from #40239.

Testing Instructions

Edit a module in the back end.

Actual result BEFORE applying this Pull Request

Error message.

Expected result AFTER applying this Pull Request

Module can be edited.

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

[brianteeman]

This fixes the error in the modules but there are lots of other changes in #40239 that need real testing and not just a sinmple code review by one person - there is a reason that we have the testing procedures that we have. And it always breaks when they are not followed

[drmenzelit]

I have tested this item ✅ successfully on 67676e5

With this patch is possible to edit and add modules again

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[laoneo]

Thank you Hannes. Unfortunately we have here the same issue as in #40131, which was moved to 5.0. I'm closing this one in favor of #40406 which reverts basically the change. As a new Exception is thrown here in a libraries file which is a BC break and should be done in 5.0.