Call set_current_screen() again in admin-header.php in case a plugin includes...

Call set_current_screen() again in admin-header.php in case a plugin includes admin-header.php before admin.php completes. Rare and silly, but seen in the wild. props ryan, see #18785.



git-svn-id: https://core.svn.wordpress.org/trunk@19522 1a063a9b-81f0-0310-95a4-ce76da25c4cd