Showing "None" when there is no session available in new tracking report

main/tracking/course_session_report.php

@@ -55,6 +55,9 @@ $my_session_list = array();
 foreach($session_list as $sesion_item) {
 	$my_session_list[$sesion_item['id']] = $sesion_item['name'];
 }
+if (count($session_list) == 0) {
+	$my_session_list[0] = get_lang('None');
+}
 $form->addElement('select', 'session_id', get_lang('Sessions'), $my_session_list);
 $form->addElement('style_submit_button','submit',get_lang('Filter'));