Prevent endless loop in \OC\Files\View::createParentDirectories

\OC\Files\View::createParentDirectories was previously prone to an endless loop. If a path such as /foo/existingfile.txt/bar/foo was passed and existingfile.txt existed in foo the loop was never left and running until the PHP process timed out.

This commit changes the logic to a foreach loop over an array and additionally additional error handling using is_file.

Signed-off-by: Lukas Reschke <lukas@statuscode.ch>