Move the "look for the first media attachment" code below the "look
in the post content for media" code, so that it is the method of last
resort. This way, if you attach AND embed media, you won't get duplication.

fixes #23879

git-svn-id: http://core.svn.wordpress.org/trunk@23840 1a063a9b-81f0-0310-95a4-ce76da25c4cd