In `gallery_shortcode()`, when the `link` attribute is equal to `file`, make sure to pass `$attr` as the 6th (!) argument, not 5th, to `wp_get_attachment_link()`.

Props bradyvercher.
Fixes #27402.


git-svn-id: https://develop.svn.wordpress.org/trunk@30161 602fd350-edb4-49c9-b593-d223f7449a82