Media: Check that a router region exists before attempting to access its child views. Add relevant documentation. see #22930.


git-svn-id: http://core.svn.wordpress.org/trunk@23260 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Media: Do not update attachment display user settings when a single attachment is inserted.

This is consistent with 3.4 behavior.

see #22841.


git-svn-id: http://core.svn.wordpress.org/trunk@23261 1a063a9b-81f0-0310-95a4-ce76da25c4cd