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>
diff --git a/archival/ar.c b/archival/ar.c
index 1b43502..4f21bf8 100644
--- a/archival/ar.c
+++ b/archival/ar.c
@@ -49,7 +49,7 @@
 	archive_handle = init_handle();
 
 	/* Prepend '-' to the first argument if required */
-	opt_complementary = "--:p:t:x:-1:p--tx:t--px:x--pt";
+	opt_complementary = "--:-1:p:t:x:-1:p--tx:t--px:x--pt";
 	opt = getopt32(argv, "ptxovcr");
 	argv += optind;
 
@@ -75,7 +75,7 @@
 		bb_error_msg_and_die(msg_unsupported_err, "insertion");
 	}
 
-	archive_handle->src_fd = xopen(argv[optind++], O_RDONLY);
+	archive_handle->src_fd = xopen(*argv++, O_RDONLY);
 
 	while (*argv) {
 		archive_handle->filter = filter_accept_list;