ref-filter: fix stale parsed objects

In 054f5f4 (ref-filter: parse objects on demand, 2025-10-23) we have
started to skip parsing some objects in case we don't need to access
their values in the first place. This was done by introducing a new
member `struct expand_data::maybe_object` that gets populated on demand
via `get_or_parse_object()`.

This has led to a regression though where the object now gets reused
because we don't reset it properly. The `oi` structure is declared in
global scope, and there is no single place where we reset it before
invoking `get_object()`. The consequence is that the `maybe_object`
member doesn't get reset across calls, so subsequent calls will end up
reusing the same object.

This is only an issue for a subset of retrieved values, as not all of
the infrastructure ends up calling `get_or_parse_object()`. So the
effect is limited, which is probably why the issue wasn't detected
earlier.

Fix the issue by resetting `maybe_object` in `get_object()`.

Reported-by: Junio C Hamano <gitster@pobox.com>
Based-on-patch-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

ref-filter.c

@@ -2367,6 +2367,8 @@ static int get_object(struct ref_array_item *ref, int deref,
 	int eaten = 0;
 	int ret;
 
+	oi->maybe_object = NULL;
+
 	if (oi->info.contentp) {
 		/* We need to know that to use parse_object_buffer properly */
 		oi->info.sizep = &oi->size;

t/t7004-tag.sh

@@ -2332,4 +2332,24 @@ test_expect_success 'If tag cannot be created then tag message file is not unlin
 	test_path_exists .git/TAG_EDITMSG
 '
 
+test_expect_success 'annotated tag version sort' '
+	git tag -a -m "sample 1.0" vsample-1.0 &&
+	git tag -a -m "sample 2.0" vsample-2.0 &&
+	git tag -a -m "sample 10.0" vsample-10.0 &&
+	cat >expect <<-EOF &&
+	vsample-1.0
+	vsample-2.0
+	vsample-10.0
+	EOF
+
+	git tag --list --sort=version:tag vsample-\* >actual &&
+	test_cmp expect actual &&
+
+	# Ensure that we also handle this case alright in the case we have the
+	# peeled values cached e.g. via the packed-refs file.
+	git pack-refs --all &&
+	git tag --list --sort=version:tag vsample-\* &&
+	test_cmp expect actual
+'
+
 test_done