transport-helper: don't feed bogus refs to export push

When we want to push to a remote helper that has the
"export" capability, we collect all of the refs we want to
push and then feed them to fast-export.

However, the list of refs is actually a list of remote refs,
not local refs. The mapped local refs are included via the
peer_ref pointer. So when we add an argument to our
fast-export command line, we must be sure to use the local
peer_ref name (and if there is no local name, it is because
we are not actually sending that ref, or we may not even
have the ref at all).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5800-remote-helpers.sh

@@ -106,7 +106,7 @@ test_expect_failure 'fetch multiple branches' '
 	compare_refs server new localclone refs/remotes/origin/new
 '
 
-test_expect_failure 'push when remote has extra refs' '
+test_expect_success 'push when remote has extra refs' '
 	(cd clone &&
 	 echo content >>file &&
 	 git commit -a -m six &&

transport-helper.c

@@ -730,7 +730,8 @@ static int push_refs_with_export(struct transport *transport,
 		}
 		free(private);
 
-		string_list_append(&revlist_args, ref->name);
+		if (ref->peer_ref)
+			string_list_append(&revlist_args, ref->peer_ref->name);
 
 	}