Pages, Post Types: Escape CSS classes in `Walker_Page::start_el()` after the `page_css_class` filter runs.

Don't add an empty `class` attribute if there are no classes, for consistency with `Walker_Nav_Menu::start_el()`.

Props abhijitrakas, mukesh27.
Fixes #44880.
Built from https://develop.svn.wordpress.org/trunk@44415


git-svn-id: http://core.svn.wordpress.org/trunk@44245 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-walker-page.php

@@ -148,6 +148,7 @@ class Walker_Page extends Walker {
 		 * @param int      $current_page ID of the current page.
 		 */
 		$css_classes = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );
+		$css_classes = $css_classes ? ' class="' . esc_attr( $css_classes ) . '"' : '';
 
 		if ( '' === $page->post_title ) {
 			/* translators: %d: ID of a post */
@@ -186,7 +187,7 @@ class Walker_Page extends Walker {
 		}
 
 		$output .= $indent . sprintf(
-			'<li class="%s"><a%s>%s%s%s</a>',
+			'<li%s><a%s>%s%s%s</a>',
 			$css_classes,
 			$attributes,
 			$args['link_before'],

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44414';
+$wp_version = '5.1-alpha-44415';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.