Fix a rare current-menu-detection bug where adding a CPT item for a CPT that doesn't have an "Add New" menu item will return null/not found, so permissions and other settings will not be applied. 

In a situation like that, WordPress highlights the edit.php?post_type=$cpt menu (if available), so it would make sense for AME to do the same.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@973268 b8457f37-d9ea-0310-8a92-e5e31aec5664