ar: fix two bugs, one added by prev comment and other we SEGV with no params

cpio: use optind less

function                                             old     new   delta
ar_main                                              189     184      -5
cpio_main                                            549     533     -16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-21)             Total: -21 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2 files changed