withRouter error, if used withOUT router

[ghost]

Version

3.0.0

Steps to reproduce

use withRouter without a Router ;) (Rendering stuff in styleguidist)
this.props.router is used only in action handlers

Expected Behavior

The component should at least render.

Actual Behavior

Get an error message:

TypeError: Cannot read property 'params' of undefined

Unfortunately, I am unable to debug in styleguidist quickly, but I think the error is coming from here:
https://github.com/ReactTraining/react-router/blob/6eeb7ad358f987520f5b519e48bdd31f725cbade/modules/withRouter.js#L32

Maybe a quick and dirty fix on Line 31 would be enough:

const router = this.props.router || this.context.router || {}

[timdorr]

We should probably just return the wrapped component:

if (!router) return <WrappedComponent {...this.props} /> 

A PR for this would be appreciated!