修改获取加价购商品详情storage_sum不存在报错的bug

@@ -590,7 +590,10 @@ class CartModel
         $data['name'] = $productData['product_name'];
         $data['price'] = $productData['market_price'];
         $data['salePrice'] = $productData['sales_price'];
+
+        if (isset($productData['storage_sum'])) {
             $data['storage'] = $productData['storage_sum'];
+        }
         if ($num !== null) {
             $data['num'] = $num;
         }