[PATCH v4 4/7] multi-pack-index: refactor "goto usage" pattern

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Refactor the "goto usage" pattern added in
cd57bc41bbc (builtin/multi-pack-index.c: display usage on unrecognized
command, 2021-03-30) and 88617d11f9d (multi-pack-index: fix potential
segfault without sub-command, 2021-07-19) to maintain the same
brevity, but in a form that doesn't run afoul of the recommendation in
CodingGuidelines about braces:

    When there are multiple arms to a conditional and some of them
    require braces, enclose even a single line block in braces for
    consistency[...]

Let's also change "argv == 0" to juts "!argv", per:

    Do not explicitly compare an integral value with constant 0 or
    '\0', or a pointer value with constant NULL[...]

I'm changing this because in a subsequent commit I'll make
builtin/commit-graph.c use the same pattern, having the two similarly
structured commands match aids readability.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/multi-pack-index.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index 8ff0dee2ecb..649aa5f9ab2 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -164,7 +164,7 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	if (!opts.object_dir)
 		opts.object_dir = get_object_directory();
 
-	if (argc == 0)
+	if (!argc)
 		goto usage;
 
 	if (!strcmp(argv[0], "repack"))
@@ -175,10 +175,9 @@ int cmd_multi_pack_index(int argc, const char **argv,
 		return cmd_multi_pack_index_verify(argc, argv);
 	else if (!strcmp(argv[0], "expire"))
 		return cmd_multi_pack_index_expire(argc, argv);
-	else {
-		error(_("unrecognized subcommand: %s"), argv[0]);
+
+	error(_("unrecognized subcommand: %s"), argv[0]);
 usage:
-		usage_with_options(builtin_multi_pack_index_usage,
-				   builtin_multi_pack_index_options);
-	}
+	usage_with_options(builtin_multi_pack_index_usage,
+			   builtin_multi_pack_index_options);
 }
-- 
2.33.0.662.gbc81f8cbdca