prevent incorrect automatic OPTIONS responses

The router has automatic handling of OPTIONS based on the registered
routes, but if you make an OPTIONS request for an endpoint that does
not exist, then it will still return a 200 with nothing allowed.
Instead, we can let the request move on down the middleware chain. This
has two benefits: first, if the route was not defined and no other
middleware handles it, it will return with a 404. Secondly, if multiple
routers are used and a later one has the route or a custom OPTIONS
defined, the first router will not respond incorrectly.