Media: Fix embedding of audio/video players when the file was just uploaded.

While uploading, we know an attachment's filename but not its mime type. Check specifically for extensions. Check for type as a convenience when it is available.

fixes #24449.



git-svn-id: http://core.svn.wordpress.org/trunk@24784 1a063a9b-81f0-0310-95a4-ce76da25c4cd