Modify the option parsing heuristic to handle all -m (rename) cases,
including the no-arg case.
Previously, this "fell through" to the (argc <= 2) case and caused
segfault.
Reported-by: Stefan Näwe <stefan.naewe@atlas-elektronik.com> Signed-off-by: Tay Ray Chuan <rctay89@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>