disable php time limit on pdf generation

When creating a large pdf from many pages it's easy to reach the default php execution time limit of 30 seconds. Hence it is disabled during pdf creation.

Author: micgro42

action.php

@@ -74,6 +74,9 @@ public function convert(Doku_Event $event) {
 
         // hard work only when no cache available
         if(!$this->getConf('usecache') || !$cache->useCache($depends)) {
+            // generating the pdf may take a long time for larger wikis / namespaces with many pages
+            set_time_limit(0);
+
             $this->generatePDF($cache->cache, $title);
         }