Relative bundle paths do not resolve properly when `--bundle-uri` has no trailing slash

[vdye]

If there's no trailing slash on a URI, Git will treat the relative path results as relative to the org part of the route, rather than relative to org/repo.

The solution here would be to serve the bundle list with the appropriate relative bundle paths, per RFC 1808. More specifically, if there's no trailing slash on the URL, we need to prepend the repo part of the route to the bundle path.