Check to see if a scale grade exists for the given grade and if not s…

…et it

to an empty string. This should never occur through normal use but just
in case ...

mod/assignment/lib.php

@@ -1294,7 +1294,11 @@ function assignment_grades($assignmentid) {
             if ($scale = get_record('scale', 'id', $scaleid)) {
                 $scalegrades = make_menu_from_list($scale->scale);
                 foreach ($grades as $key => $grade) {
-                    $grades[$key] = $scalegrades[$grade];
+                    if (empty($scalegrades[$key])) {
+                        $grades[$key] = '';
+                    } else {
+                        $grades[$key] = $scalegrades[$grade];
+                    }
                 }
             }
         }