Fix deprecation notices caused by tag_escape

https://wordpress.org/support/topic/php-deprecated-preg_replace-passing-null-to-parameter-3/

Author: klemens-st

include/lcp-catlistdisplayer.php

@@ -261,7 +261,8 @@ public function get_post_title($single, $tag = null, $css_class = null,
     }
 
     // Shortcode parameters take precedence.
-    $tag = tag_escape($this->params['title_tag']) ?: tag_escape($tag);
+    $tag = $this->params['title_tag'] ?: $tag;
+    $tag = $tag ? tag_escape($tag) : $tag;
     $css_class = esc_attr($this->params['title_class']) ?: esc_attr($css_class);
     $suffix = $this->params['post_suffix'] ? ' ' . $this->params['post_suffix'] : '';