options: Fix getopts handling of colon in optstr

Putting a colon at the beginning of optstring to silence errors doesn't
mean that the colon is a valid option. Before this patch, dash treated
-: as a valid option if the optstring started with a colon. This patch
fixes that problem.

Test:

    getopts :a opt -:
    echo $opt$OPTARG

Correct output - ?:
Invalid output - :

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/options.c b/src/options.c
index e192191..8101cf5 100644
--- a/src/options.c
+++ b/src/options.c
@@ -467,7 +467,7 @@ atend:
 	}
 
 	c = *p++;
-	for (q = optstr; *q != c; ) {
+	for (q = optstr[0] == ':' ? optstr + 1 : optstr; *q != c; ) {
 		if (*q == '\0') {
 			if (optstr[0] == ':') {
 				s[0] = c;