MDL-36966 Assignment: Bug - Student submission appears graded by themselves.

Fix a bug when a student editing his submission after it has been graded, it changes the 'graded by' details to the student's name in the feeback summary

mod/assign/locallib.php

@@ -2874,7 +2874,7 @@ class assign {
                 }
 
                 $gradeddate = $gradebookgrade->dategraded;
-                $grader = $DB->get_record('user', array('id'=>$gradebookgrade->usermodified));
+                $grader = $DB->get_record('user', array('id'=>$grade->grader));
 
                 $feedbackstatus = new assign_feedback_status($gradefordisplay,
                                                       $gradeddate,