vue-loader compile error when use with loader has `enforce: post`

[zhuzhuaicoding]

Version

15.2.1

Reproduction link

https://github.com/earlymeme/test-vue-loader-with-post-loader

Steps to reproduce

1. run yarn to install devDependencies
2. run yarn test to create a test server
3. open your url

What is expected?

no error

What is actually happening?

Uncaught TypeError: Cannot set property 'render' of undefined
at normalizeComponent (componentNormalizer.js?2877:24)

---

loaders[0] is not self in this case. https://github.com/vuejs/vue-loader/blob/v15.2.1/lib/loaders/pitcher.js#L23
because of https://github.com/webpack/webpack/blob/v4.12.1/lib/NormalModuleFactory.js#L318 the post loader will be the first one.