Bug #1588091: Fix 'name display format' issue

When a user chooses the 'name_display_format' of studentid
- we get an error.

This change just populates the studentid field of the user

behatnotneeded

Change-Id: I1e6a84723863e49dd94b83cb115f26262e6d9750

htdocs/lib/user.php

@@ -1223,6 +1223,7 @@ function get_user_for_display($user=null) {
     $fields = array(
         'id', 'username', 'preferredname', 'firstname', 'lastname', 'admin', 'staff',
         'profileicon', 'email', 'deleted', 'urlid', 'suspendedctime',
+        'studentid',
     );
 
     if (is_numeric($user) && isset($usercache[$user])) {