[PATCH] options: Fix getopts handling of colon in optstr

[Subhaditya Nath <sn03.general@xxxxxxxxx>]

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 - :
---
 src/options.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/options.c b/src/options.c
index 2d4bd3b..8593710 100644
--- a/src/options.c
+++ b/src/options.c
@@ -465,7 +465,7 @@ 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;
-- 
2.39.1