### What?
When using rewrites, in the scenario where a user visits an intercepted
route, reloads the page, goes back, and then revisits the same route, we
serve the page rather than the intercepted route.
### Why?
#59094 fixed the case where `ACTION_RESTORE` was not restoring `nextUrl`
properly. However there's a separate issue where when the `SERVER_PATCH`
action comes in, `handleMutable` attempts to compute `nextUrl` by
comparing the patched tree with the current tree. In the case of the
popstate event, both trees are the same, so the logic is currently
configured to fallback to `canonicalUrl`, which is not the correct URL
to use in the case of rewrites.
### How?
If the computed changed path is null, we should only fallback to using
`canonicalUrl` if we don't have a valid `nextUrl` that we can use.
Closes NEXT-1747
Fixes#56072
5f98e9bc6e