Media: When inserting an attachment, if the item is unattached (no...

Media: When inserting an attachment, if the item is unattached (no post_parent), attach it to the post. fixes #22085.



git-svn-id: https://core.svn.wordpress.org/trunk@22843 1a063a9b-81f0-0310-95a4-ce76da25c4cd