HTML API: Call $this->is_tag_closer() in HTML Processor.

The HTML Processor had been calling the parent class `is_tag_closer()`
method, but since visiting virtual nodes was introduced, it's important
that all of the methods are called on the subclass.

This patch fixes one issue identified where the parent method was called
instead, and it fixes another case where the change from calling the
parent method to the `$this` method was done improperly.

Developed in #6726
Discussed in https://core.trac.wordpress.org/ticket/61348

Props jonsurrell.
See #61348.
Follow-up to [58304].


git-svn-id: https://develop.svn.wordpress.org/trunk@58365 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/html-api/class-wp-html-processor.php

@@ -429,7 +429,7 @@ public function next_tag( $query = null ) {
 					continue;
 				}
 
-				if ( ! $this::is_tag_closer() || $visit_closers ) {
+				if ( ! $this->is_tag_closer() || $visit_closers ) {
 					return true;
 				}
 			}
@@ -464,7 +464,7 @@ public function next_tag( $query = null ) {
 					continue;
 				}
 
-				if ( ! parent::is_tag_closer() || $visit_closers ) {
+				if ( ! $this->is_tag_closer() || $visit_closers ) {
 					return true;
 				}
 			}