Add validation to Merchant Order Controller update

lib/shotengai/controllers/merchant/product_snapshots_controller.rb

@@ -19,6 +19,11 @@ module Shotengai
             )
         end
 
+        def update
+          raise Shotengai::WebError.new('订单已支付，不可修改。', '-1', 403) unless @resource.order.unpaid?
+          super
+        end
+
         private
           def resource_params
             params.require(resource_key).permit(