Merge branch 'rb/http-cert-cred-no-username-prompt'

http transport was wrong to ask for the username when the
authentication is done by certificate identity.

* rb/http-cert-cred-no-username-prompt:
  http.c: Avoid username prompt for certifcate credentials

http.c

@@ -236,6 +236,7 @@ static int has_cert_password(void)
 		return 0;
 	if (!cert_auth.password) {
 		cert_auth.protocol = xstrdup("cert");
+		cert_auth.username = xstrdup("");
 		cert_auth.path = xstrdup(ssl_cert);
 		credential_fill(&cert_auth);
 	}