修复结算页切换运送方式时YOHO币会显示错乱的bug；修复使用免邮券不显示的bug

Code Review By Rock Zhang

@@ -14,7 +14,7 @@ function init() {
         deliveryId: 1,
         deliveryTimeId: 1,
         paymentTypeId: 1,
-        yohoCoin: $('.coin').data('yoho-coin') || 0,
+        yohoCoin: 0,
         addressId: null,
         couponCode: null,
         couponName: null,

@@ -486,7 +486,7 @@ class CartModel
 
             // 优惠券数据
             $coupons = array('couponName' => '');
-            if (!empty($orderCompute['coupon_amount'])) {
+            if (isset($orderCompute['coupon_amount']) && (!empty($orderCompute['coupon_amount']) || ($orderCompute['coupon_amount'] === 0 && $orderCompute['shipping_cost'] === 0))) {
                 $coupons['couponName'] = $orderInfo['couponName'];
             }
             $result['coupon'] = $coupons;