[GolemBridge] Add multi-page headings

On multi-page articles like [1], some paragraph headers were missing
because they are headers of the article pages.

These headers were previously removed in
c5f586497f for being redundant with the
original header. The article at [1] proves us wrong, but I added a logic
to ignore truly duplicate headers.

[1] https://www.golem.de/news/es-muss-nicht-immer-apple-sein-fuenf-ueberzeugende-airpods-pro-alternativen-im-test-2508-195000.html

bridges/GolemBridge.php

@@ -132,13 +132,22 @@ class GolemBridge extends FeedExpander
         // delete known bad elements
         foreach (
             $article->find('div[id*="adtile"], #job-market, #seminars, iframe,
-			.gbox_affiliate, div.toc') as $bad
+                        .gbox_affiliate, div.toc') as $bad
         ) {
             $bad->remove();
         }
         // reload html, as remove() is buggy
         $article = str_get_html($article->outertext);
 
+        // Add multipage headers, but only if they are different to the article header
+        $firstHeader = $page->find('.table-jtoc td', 0);
+        if (isset($firstHeader)) {
+            $firstHeader = html_entity_decode($firstHeader->title);
+        }
+        $multipageHeader = $article->find('header.paged-cluster-header h1', 0);
+        if (isset($multipageHeader) && $multipageHeader->plaintext !== $firstHeader) {
+            $item .= $multipageHeader;
+        }
 
         $header = $article->find('header', 0);
         foreach ($header->find('p, figure') as $element) {