修复券后金额为负数

pages/make_order/make_order/make_order.wxml

@@ -135,7 +135,7 @@
     <view class="cacu">
       <text class="text">实付款</text>
       <text decode="{{true}}" class="fee">&nbsp;&nbsp;¥</text>
-      <text decode="{{true}}" class="fee1">{{coupon?(_info.order_info.order_price-coupon.subtract):_info.order_info.order_price}}&nbsp;&nbsp;</text>
+      <text decode="{{true}}" class="fee1">{{coupon?((_info.order_info.order_price-coupon.subtract>=0)?(_info.order_info.order_price-coupon.subtract):0):_info.order_info.order_price}}&nbsp;&nbsp;</text>
       <text class="detail" bindtap="de">明细{{fee_detail?'▼':'▲'}}</text>
     </view>
     <button class="button" bindtap="onSubmit">提交订单</button>
@@ -161,7 +161,7 @@
     </view>
     <view class="ln">
       <view>支付金额：</view>
-      <view>¥{{coupon?(_info.order_info.order_price-coupon.subtract):_info.order_info.order_price}}</view>
+      <view>¥{{coupon?((_info.order_info.order_price-coupon.subtract>=0)?(_info.order_info.order_price-coupon.subtract):0):_info.order_info.order_price}}</view>
     </view>
     <view class="ln">
       <view>购票数：</view>