star repo: Check for url safety only when referrer is there
    
    While testing, the referrer is not there and pagure.is_safe_url
    return True in case the referrer is not there. Thus, it used to
    give 404s instead of returning to index
    
    Signed-off-by: Vivek Anand <vivekanand1101@gmail.com></vivekanand1101@gmail.com>