builtin/repack.c: ensure that `names` is sorted

The previous patch demonstrates a scenario where the list of packs
written by `pack-objects` (and stored in the `names` string_list) is
out-of-order, and can thus cause us to delete packs we shouldn't.

This patch resolves that bug by ensuring that `names` is sorted in all
cases, not just when

    delete_redundant && pack_everything & ALL_INTO_ONE

is true.

Because we did sort `names` in that case (which, prior to `--geometric`
repacks, was the only time we would actually delete packs, this is only
a bug for `--geometric` repacks.

It would be sufficient to only sort `names` when `delete_redundant` is
set to a non-zero value. But sorting a small list of strings is cheap,
and it is defensive against future calls to `string_list_has_string()`
on this list.

Co-discovered-by: Victoria Dye <vdye@github.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/repack.c

@@ -856,6 +856,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	if (!names.nr && !po_args.quiet)
 		printf_ln(_("Nothing new to pack."));
 
+	string_list_sort(&names);
+
 	for_each_string_list_item(item, &names) {
 		item->util = (void *)(uintptr_t)populate_pack_exts(item->string);
 	}
@@ -896,7 +898,6 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 
 	if (delete_redundant && pack_everything & ALL_INTO_ONE) {
 		const int hexsz = the_hash_algo->hexsz;
-		string_list_sort(&names);
 		for_each_string_list_item(item, &existing_nonkept_packs) {
 			char *sha1;
 			size_t len = strlen(item->string);

t/t7703-repack-geometric.sh

@@ -231,7 +231,7 @@ test_expect_success '--geometric chooses largest MIDX preferred pack' '
 	)
 '
 
-test_expect_failure '--geometric with pack.packSizeLimit' '
+test_expect_success '--geometric with pack.packSizeLimit' '
 	git init pack-rewrite &&
 	test_when_finished "rm -fr pack-rewrite" &&
 	(