Fix auth sample login route (#3918)
Fix auth sample login route (#3918)

Attempting to visit the /login route directly results in a "this.props.location.state is null" error which breaks the example.  This fix tells the app that it came from the base route if it is not the result of a redirect.
OpenGov/react-router,reactjs/react-router,ReactTraining/react-router,rafrex/react-router,asaf/react-router,asaf/react-router,OpenGov/react-router,ReactTraining/react-router,goblortikus/react-router,goblortikus/react-router,rackt/react-router,DelvarWorld/react-router,rackt/react-router,reactjs/react-router,goblortikus/react-router,asaf/react-router,goblortikus/react-router,ReactTraining/react-router,OpenGov/react-router,rafrex/react-router,DelvarWorld/react-router,d-oliveros/react-router,ReactTraining/react-router,OpenGov/react-router,d-oliveros/react-router