[BUGFIX] Handle if some tags are upper-case and strict-comparison

The method getTagContent in class HtmlContentExtractor should also for
work for tags that are not lower case.

Resolves: #3940

Classes/HtmlContentExtractor.php

@@ -224,7 +224,8 @@ public function getTagContent(): array
         foreach ($matches[1] as $key => $tag) {
             // We don't want to index links auto-generated by the url filter.
             $pattern = '@(?:http://|https://|ftp://|mailto:|smb://|afp://|file://|gopher://|news://|ssl://|sslv2://|sslv3://|tls://|tcp://|udp://|www\.)[a-zA-Z0-9]+@';
-            if ($tag != 'a' || !preg_match($pattern, $matches[2][$key])) {
+            $tag = strtolower((string)$tag);
+            if ($tag !== 'a' || !preg_match($pattern, $matches[2][$key])) {
                 $fieldName = $this->tagToFieldMapping[$tag];
                 $hasContentForFieldName = empty($result[$fieldName]);
                 $separator = ($hasContentForFieldName) ? '' : ' ';