Bug: add missing event listener for PM

Neither of the other two already registered events would get fired while writing a PM; the new listener code should nw deal with PMs as well (and very likely Quick Reply, too)

Author: GwynethLlewelyn

gwynethllewelyn/postlocalstorage/event/listener.php

@@ -64,6 +64,7 @@ static public function getSubscribedEvents()
 		return [
 			'core.modify_submit_post_data'      => 'check_expiry_time',
 			'core.posting_modify_template_vars' => 'check_expiry_time',
+			'core.ucp_pm_compose_template'		=> 'check_expiry_time',
 		];
 	}