[ticket/11777] Require a suffix of '_listener' on extension template listeners

To further mirror the file name and location requirements for php template
event listeners, require extension template event listener files to follow the
'<event name>_listener.html' naming format.

PHPBB3-11777

phpBB/phpbb/template/twig/node/event.php

@@ -43,7 +43,7 @@ class phpbb_template_twig_node_event extends Twig_Node
 	{
 		$compiler->addDebugInfo($this);
 
-		$location = $this->listener_directory . $this->getNode('expr')->getAttribute('name');
+		$location = $this->listener_directory . $this->getNode('expr')->getAttribute('name') . '_listener';
 
 		foreach ($this->environment->get_phpbb_extensions() as $ext_namespace => $ext_path)
 		{