URL params are not available inside middleware on the root router

When I create a middleware to log the `id` URL parameter, which exists in the route I request, the value is always empty. I do get a value inside the handler itself

```Go
r := chi.NewRouter()

r.Use(func(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
id := chi.URLParam(r, "id")
log.Println(id)
h.ServeHTTP(w, r)
})
})

r.Get("/test/{id}", func(w http.ResponseWriter, r *http.Request) {
id := router.Param(r, "id").String()
io.WriteString(w, id)
})
```

When I move this code to a `Group`, the URL param will become available inside the middleware.

```Go
r := chi.NewRouter()

r.Group(func(r chi.Router) {
r.Use(func(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
id := chi.URLParam(r, "id")
log.Println(id)
h.ServeHTTP(w, r)
})
})

r.Get("/test/{id}", func(w http.ResponseWriter, r *http.Request) {
id := router.Param(r, "id").String()
io.WriteString(w, id)
})
})
```

I think this behavior is quite strange and prone to errors

Tested with the latest version (5.0.11)