for-each-ref: Fix sort with multiple keys

The linked list describing sort options was not correctly set up in
opt_parse_sort. In the result, contrary to the documentation, only the
last of multiple --sort options to git-for-each-ref was taken into
account. This commit fixes it.

Signed-off-by: Kacper Kornet <draenog@pld-linux.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/for-each-ref.c

@@ -962,7 +962,9 @@ static int opt_parse_sort(const struct option *opt, const char *arg, int unset)
 	if (!arg) /* should --no-sort void the list ? */
 		return -1;
 
-	*sort_tail = s = xcalloc(1, sizeof(*s));
+	s = xcalloc(1, sizeof(*s));
+	s->next = *sort_tail;
+	*sort_tail = s;
 
 	if (*arg == '-') {
 		s->reverse = 1;

t/t6300-for-each-ref.sh

@@ -461,7 +461,7 @@ cat >expected <<\EOF
 90b5ebede4899eda64893bc2a4c8f1d6fb6dfc40 <committer@example.com> refs/tags/bogo
 EOF
 
-test_expect_failure 'Verify sort with multiple keys' '
+test_expect_success 'Verify sort with multiple keys' '
 	git for-each-ref --format="%(objectname) %(taggeremail) %(refname)" --sort=objectname --sort=taggeremail \
 		refs/tags/bogo refs/tags/master > actual &&
 	test_cmp expected actual