Prevent crash if a user edits a group and gives it the same name as an existing group.

htdocs/group/edit.php

@@ -89,7 +89,7 @@ function editgroup_validate(Pieform $form, $values) {
     global $USER;
     global $SESSION;
 
-    $cid = get_field('group', 'id', 'owner', $USER->get('id'), 'name', $values['name']);
+    $cid = get_field('group', 'id', 'name', $values['name']);
 
     if ($cid && $cid != $values['id']) {
         $form->set_error('name', get_string('groupalreadyexists', 'group'));