Fix controller spec fails on edge Rails

Current edge Rails split named_routes.helpers to path_helpers and url_helpers.
And add `route_defined?` method to NamedRouteCollection.
Because of it, Controller Spec is failed on edge Rails.
This patch fixes it.

refs.
- https://github.com/rails/rails/commit/f889831ed65bea14b6b687bdaa4012d73d81b2a6
- https://github.com/rails/rails/commit/210b338db20b1cdd0684f40bd78b52ed16148b99

I think we can improve this by returning false early if `routes` is `nil`.

```ruby
def route_defined?(routes, method)
  return false if routes.nil?
  # ...
end
```

Then we can reduce the method missing to a single `if`/`else`:

```ruby
def method_missing(method, *args, &block)
  if route_available?(method)
    controller.send(method, *args, &block)
  else
    super
  end
end

private

def route_available?(method)
  ( defined?(@routes) && route_defined?(routes, method) ) ||
    ( defined?(@orig_routes) && route_defined?(@orig_routes, method) )
end
```

/cc @JonRowe thoughts?