Improve error catching flow in "Defining Your Routes: Wildcard/Globbing Routes" guide section

Guide: https://guides.emberjs.com/release/routing/defining-your-routes/#toc_wildcard--globbing-routes

> The error catching flow in https://guides.emberjs.com/release/routing/defining-your-routes/#toc_wildcard--globbing-routes is not ideal, it swallows all errors silently. Also, promise API is being used inside an `async` function which is not needed.
(at)mixonic