[BUGFIX] Canonicalize path before checking existence

ResourceFactory fails to detect files in symlinked
scenarios, because the path is not canonicalized before
file existence is checked.

Solution is to canonicalize it and check then.

Resolves: #59303
Releases: 6.2
Change-Id: I4fd763f7076e909f2163af79ed2b7f8642da8ed7
Reviewed-on: https://review.typo3.org/30532
Reviewed-by: Markus Klein
Tested-by: Markus Klein