[examples] core_directory_files fixes

[hugoarnal]

Fixed the following issues:

• When clicking on a folder, the index can be superior to the count of the new entered folder which instantly crashes the example
• Char devices (such as the ones in /dev) can be clicked even though they are not directories.

[hugoarnal]

For some reason CI absolutely wants to push rlparser even though I'm based on master which should ignore it 🤔

[raysan5]

@hugoarnal Please, could you remove rlparser binary?

EDIT: Just saw it's automatically added by the CI Workflow but it's strange because that workflow should only run on raylib.h updates...

[raysan5]

@hugoarnal Just reviewed it myself and merged