[config] Directory path not working without trailing slash

[MaximeMulder]

Describe the bug

While testing #9203, I noticed that if I do not put a trailing slash at the end of the media path (example: /data/media instead of /data/media/), the path is accepted but I get an error 500 while uploading the file later.

I haven't yet looked at how config works and if other paths are affected, but ideally the behaviour should be the same for all directory paths, which should have a trailing slash automatically appended if it is not already present.