MDL-41149 assign: Group submission updates emailed to wrong person

grade_item_update was altering the userid in the submission record
instead of cloning it. This meant only the last member of a group
recieved all notifications meant for other students in the group.

mod/assign/locallib.php

@@ -3907,9 +3907,10 @@ class assign {
                 $team = groups_get_members($submission->groupid, 'u.id');
 
                 foreach ($team as $member) {
-                    $submission->groupid = 0;
-                    $submission->userid = $member->id;
-                    $this->gradebook_item_update($submission, null);
+                    $membersubmission = clone $submission;
+                    $membersubmission->groupid = 0;
+                    $membersubmission->userid = $member->id;
+                    $this->gradebook_item_update($membersubmission, null);
                 }
                 return;
             }