Cannot read property 'status' of undefined error when there is no network

When there is no network the `_request` function fails, without rejecting the Promise, which makes impossible to catch the error when using a callback.

Even though the component can't be used without the network (#388), I think would be good to handle the case.

The error:

`TypeError: Cannot read property 'status' of undefined`

首先定位 `_request` 函数，并复现 issue 中描述的无网络情况。检查 issue #388 中的相关上下文，然后确保失败的请求 reject 其 Promise，以便 callback 用户能够捕获错误；当未定义的 `status` 错误得到处理而不是逸出时，即表示完成。

由索引模型根据 Issue 内容生成。