When an HTML5 fallback button is pressed in the Audio or Video Details state, filter the library by that specific mime-type when the Add Audio|Video Source is activated.

See #27389.


Built from https://develop.svn.wordpress.org/trunk@27658


git-svn-id: http://core.svn.wordpress.org/trunk@27501 1a063a9b-81f0-0310-95a4-ce76da25c4cd