Getting router routes fails on node

[meztez]

a <- pr()
pr_get(a, "/__swagger__/", to_route("../__docs__/"))
pr_get(a, "/__swagger__/index.html", to_route("../__docs__/index.html"))
a$routes
 Error in node[[children[1]]] <- addPath(node[[children[1]]], children[-1],  : 
  cannot add bindings to a locked environment 
>

Describe the problem in detail

Discovered while using $routes on a router with mounted redirects working on #694.

[schloerke]

Fixed in #702