fix: #2938

[hailaz]

fix #2938
如果需要body支持复读，可以在前置中间件中使用r.MakeBodyRepeatableRead(true)

s.Group("/", func(group *ghttp.RouterGroup) {
		group.Middleware(func(r *ghttp.Request) {
			fmt.Println("middleware")
			r.MakeBodyRepeatableRead(true)
			r.Middleware.Next()
		})
		group.Middleware(ghttp.MiddlewareHandlerResponse)
		group.Bind(cUpload{})
	})