Allow empty router to pass to next middleware
Allow empty router to pass to next middleware

When no router is defined for a feature app the default needs to
just call next to allow the app to pass through.

uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend,uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend,uktrade/data-hub-frontend