restore missing parameter, re #70

exercises/tb_exercise.php

@@ -181,7 +181,7 @@ class tb_exercise extends Exercise
     /**
      * Trigger download of uploaded file for a selected solution.
      */
-    public function download_action()
+    public function download_action($controller)
     {
         vips_require_status('autor');
 
@@ -215,7 +215,7 @@ class tb_exercise extends Exercise
     /**
      * Trigger download of all uploaded files for a selected solution.
      */
-    public function download_zip_action()
+    public function download_zip_action($controller)
     {
         vips_require_status('autor');