Eliminate use of `extract()` in `get_media_item()`.
	
To test, fire open the old media in the console: `tb_show('Old Media is Weird', 'media-upload.php?type=image&TB_iframe=true&post_id=0');`	
	
See #22400.


git-svn-id: https://develop.svn.wordpress.org/trunk@28407 602fd350-edb4-49c9-b593-d223f7449a82