Prior to this change, if a navigation was ongoing and a new one came in, the router could get into a state where `router.currentNavigation` was `null` even though a navigation was executing. This change moves where we set the `currentNavigation` value so it's inside a `switchMap`. This solves the problem because the `finally` on the `switchMap` had been setting `currentNavigation` to `null` but the new `currentNavigation` value would have already been set. Essentially this was a timing problem and is resolved with this change.
Fixes#29389#29590
PR Close#29636
f9497bf28b