Fix a variable typo in `get_post_gallery_images()`.

props rodrigosprimo. Fixes #24202 for trunk.

git-svn-id: https://core.svn.wordpress.org/trunk@24837 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.7-alpha-24839.

git-svn-id: https://core.svn.wordpress.org/trunk@24839 1a063a9b-81f0-0310-95a4-ce76da25c4cd