Don't show Appearance > Widgets if the theme has no sidebars defined. props SergeyBiryukov for the initial patch. fixes #21761.

git-svn-id: https://develop.svn.wordpress.org/trunk@21825 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/functions.php

@@ -2549,6 +2549,10 @@ function wp_maybe_load_widgets() {
  */
 function wp_widgets_add_menu() {
 	global $submenu;
+
+	if ( ! current_theme_supports( 'widgets' ) )
+		return;
+
 	$submenu['themes.php'][7] = array( __( 'Widgets' ), 'edit_theme_options', 'widgets.php' );
 	ksort( $submenu['themes.php'], SORT_NUMERIC );
 }