Don't try to load WP in admin-ajax if we have no action to take.

git-svn-id: https://develop.svn.wordpress.org/trunk@15606 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/admin-ajax.php

@@ -14,11 +14,11 @@
 define('DOING_AJAX', true);
 define('WP_ADMIN', true);
 
-require_once('../wp-load.php');
-
 if ( ! isset( $_REQUEST['action'] ) )
 	die('-1');
 
+require_once('../wp-load.php');
+
 require_once('./includes/admin.php');
 @header('Content-Type: text/html; charset=' . get_option('blog_charset'));
 send_nosniff_header();