gotwebd: add the magic ".git" handling
like gotd, assume an implicit ".git" if the repo doesn't exist.
Merge gotweb_init_repo_dir() and gotweb_load_got_path() since the
former only sets repo_dir->name, and we don't realistically know
the name until we've opened the directory.
While here, unbreak the git worktree handling too.
Realistically, moving forward, we should issue a redirect to the
canonical URL or at least set the correct metadata in the document
to avoid having multiple URLs for the same content.
ok stsp; tiny change to repo_dir->name handling done after the ok.