misc/opts.c: fix string handling
fixes usage string of poly, for example
@@ -832,7 +832,7 @@ static int add_tuple_args(int bufsize, char buf[static bufsize], const struct ar
pos += xsnprintf(bufsize - pos, buf + pos, " ");
}
- pos += snprintf(buf + pos, pos, "... ");
+ pos += xsnprintf(bufsize - pos, buf + pos, "... ");
for (int k = 0; k < arg->nargs; ++k ) {
