There was bug in parsing "project/:/file" and "project/:/" path_info
URLs, with implicit HEAD as 'hash_base'.
For such URLs the refname is empty, and before this fix regexp for
parsing path_info fragment assumed that it is always non-empty.
Refname cannot contain ':', as per 'git check-ref-format'.
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>