fix special id bug

helper/activity/optional_goods.php

@@ -30,7 +30,7 @@ class opgroup
         $this->mStartTm = $start;
         $this->mEndTm = $end;
         $this->mRepeat = $repeat;
-        $this->mSpecialID;
+        $this->mSpecialID = $special_id;
 
         $this->mGoods = [];
     }