Because gitlab way of passing project ID as user/project URL-encoded does not support dots (it would needs to be encoded as %2E) and that requests rewrites %2F from URL to . (which is probably correct, that's the RFC), we cannot use encoded paths for when they contain a dot.
To workaround this, when user or repo as a dot, make another API call to get the numerical project ID and use that instead.
We only do that for projects with a dot because that's an extra request we'd like to avoid.