It seems that the purpose of the stanza is as the comment says - prevent loading directories.  If we have an album, only its thumb exists as a file.  The old version prevented the "albums" directory of an album, but not the "resizes" directory even though there's nothing there to see.

That said, it's a somewhat trivial change because it'll 404 a few stanzas later (if (!file_exists($file))).  This is because the resize_path of an album is given an imaginary filename similar to the thumb_path (but dissimilar from the file_path for some reason).  So, it was a matter of prettiness - reject based on a good reason or reject by default with an imaginary filename <shrug>.