Prevent a PHP Warning for $post_format.

props MZAWeb, kovshenin. see #24011.

git-svn-id: http://core.svn.wordpress.org/trunk@24094 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.6-beta1-24095.

git-svn-id: http://core.svn.wordpress.org/trunk@24095 1a063a9b-81f0-0310-95a4-ce76da25c4cd