Flat URL redirect ignores site

[mbrodala]

Given two sites one and two with two pages with UID 1 and 2 respectively. When accessing https://one.example.org/2, a flat URL redirect to https://one.example.org/2-slug is triggered. However, if the page with UID 2 is within site two, then the result is a 404.

While this is technically correct the behavior should be adjusted to either of these:

1. The initial request directly yields a 404 without redirect (the example above would stay at https://one.example.org/2)
2. The redirect includes the target site base to actually work (the example above would redirect to https://two.example.org/2-slug)