Prevent error when updating status when student marking disabled.

defaultstatus.php

@@ -100,7 +100,7 @@ switch ($action) {
         $acronym        = required_param_array('acronym', PARAM_TEXT);
         $description    = required_param_array('description', PARAM_TEXT);
         $grade          = required_param_array('grade', PARAM_RAW);
-        $studentavailability = required_param_array('studentavailability', PARAM_RAW);
+        $studentavailability = optional_param_array('studentavailability', '0', PARAM_RAW);
         $unmarkedstatus = optional_param('setunmarked', null, PARAM_INT);
         foreach ($grade as &$val) {
             $val = unformat_float($val);
@@ -113,6 +113,9 @@ switch ($action) {
             if ($unmarkedstatus == $id) {
                 $setunmarked = true;
             }
+            if (!isset($studentavailability[$id])) {
+                $studentavailability[$id] = 0;
+            }
             $errors[$id] = attendance_update_status($status, $acronym[$id], $description[$id], $grade[$id],
                                              null, null, null, $studentavailability[$id], $setunmarked);
         }