Redering 200 when it should render empty CSS

Example app:

```
/main.less
/200.jade
```

When `/main.less` has content it renders fine, but if there are no styles, then it renders the 200.jade.

**Expected behaviour:**
It should render an empty CSS file if it exists with `text/css` as the Content Type.

**Current behaviour:**
It's returning the type as `text/html` and the content of the 200.jade