Customize: Make sure that preview and return URLs are URLs.

Merge of [37527] to the 4.2 branch.
Built from https://develop.svn.wordpress.org/branches/4.2@37772


git-svn-id: http://core.svn.wordpress.org/branches/4.2@37737 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/customize.php

@@ -18,9 +18,11 @@ if ( ! current_user_can( 'customize' ) ) {
 
 wp_reset_vars( array( 'url', 'return' ) );
 $url = wp_unslash( $url );
+$url = esc_url_raw( $url );
 $url = wp_validate_redirect( $url, home_url( '/' ) );
 if ( $return ) {
 	$return = wp_unslash( $return );
+	$return = esc_url_raw( $return );
 	$return = wp_validate_redirect( $return );
 }
 if ( ! $return ) {