Customizer: Restore default `fallback_cb` arg for `wp_nav_menu()` calls in customizer preview.

Props ocean90, westonruter.
Fixes #33218.

Built from https://develop.svn.wordpress.org/trunk@33585


git-svn-id: http://core.svn.wordpress.org/trunk@33552 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/nav-menu-template.php

@@ -230,11 +230,6 @@ function wp_nav_menu( $args = array() ) {
 	'echo' => true, 'fallback_cb' => 'wp_page_menu', 'before' => '', 'after' => '', 'link_before' => '', 'link_after' => '', 'items_wrap' => '<ul id="%1$s" class="%2$s">%3$s</ul>',
 	'depth' => 0, 'walker' => '', 'theme_location' => '' );
 
-	// Prevent a fallback_cb in Customizer Preview to assist with has_nav_menu() and partial refresh.
-	if ( is_customize_preview() ) {
-		$defaults['fallback_cb'] = '';
-	}
-
 	$args = wp_parse_args( $args, $defaults );
 	/**
 	 * Filter the arguments used to display a navigation menu.

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-RC2-33584';
+$wp_version = '4.3-RC2-33585';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.