MDL-66147 mod_assign: grading table status col shows relative dates

The 'Status' column is sorted using 'status ASC/DESC, userid ASC',
where status does not contain the due date. Overdue assignments
have additional information displayed, but this is unrelated to
the sort, meaning we don't need to change anything with sorting.

mod/assign/gradingtable.php

@@ -1034,7 +1034,7 @@ class assign_grading_table extends table_sql implements renderable {
     public function col_status(stdClass $row) {
         $o = '';
 
-        $instance = $this->assignment->get_instance();
+        $instance = $this->assignment->get_instance($row->userid);
 
         $due = $instance->duedate;
         if ($row->extensionduedate) {