Geo secondary proxying: pull through HTTP(s) redirect loop when repository doesn't exist

As found in &6418 (comment 707928780), if the project exists in the DB but its repository isn't synced yet, or has failed, such as there is no repository on the secondary, git HTTP operations will get into a redirect loop:

Cloning into 'project'...
fatal: unable to access 'http://unified.url/project.git/': Maximum (20) redirects followed

Using GIT_CURL_VERBOSE=1 we can see the redirect loop happens in /project.git/info/refs?service=git-upload-pack