Use correct activity name in otification email subject

htdocs/lib/activity.php

@@ -88,6 +88,7 @@ function handle_activity($activitytype, $data, $cron=false) {
     $data = $activity->to_stdclass();
     safe_require('notification', 'internal', 'lib.php', 'require_once');
     $data->type = $activity->get_id();
+    $data->activityname = $activitytype->name;
     foreach ($activity->get_users() as $user) {
         $userdata = $data;
         // some stuff gets overridden by user specific stuff

htdocs/notification/email/lib.php

@@ -33,7 +33,7 @@ class PluginNotificationEmail extends PluginNotification {
     public static function notify_user($user, $data) {
 
         $sitename = get_config('sitename');
-        $fulltype = get_string('type' . $data->type, 'activity');
+        $fulltype = get_string('type' . $data->activityname, 'activity');
         $subject = get_string('emailsubject', 'notification.email', $sitename, $fulltype);
         if (!empty($data->subject)) {
             $subject .= ': ' . $data->subject;