In `Walker_Category::start_el()`, `$title` might not be set when `$args` are passed multiple levels into `walk_category_tree()`.

See #22400.


Built from https://develop.svn.wordpress.org/trunk@28438


git-svn-id: http://core.svn.wordpress.org/trunk@28265 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/category-template.php

@@ -1001,7 +1001,7 @@ class Walker_Category extends Walker {
 			} else {
 				$alt = ' alt="' . $args['feed'] . '"';
 				$name = $args['feed'];
-				$link .= $args['title'];
+				$link .= empty( $args['title'] ) ? '' : $args['title'];
 			}
 
 			$link .= '>';