调整下单砍价优惠默认值

app/Services/OrderService.php

@@ -226,7 +226,7 @@ class OrderService
                     'consignee_zone' => $shippingAddress->zone,
                     'consignee_address' => $shippingAddress->address,
                     //砍价订单金额
-                    'bargain_amount'=>$bargainOrder?->bargain_price,
+                    'bargain_amount'=>$bargainOrder?->bargain_price ?? 0,
                 ];
 
                 return $user->orders()->create($attrs);