commit-graph: early exit to "usage" on !argc

Rather than guarding all of the !argc with an additional "if" arm
let's do an early goto to "usage". This also makes it clear that
"save_commit_buffer" is not needed in this case.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -331,16 +331,17 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 			     builtin_commit_graph_options,
 			     builtin_commit_graph_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
+	if (!argc)
+		goto usage;
 
 	save_commit_buffer = 0;
 
-	if (argc > 0) {
-		if (!strcmp(argv[0], "verify"))
-			return graph_verify(argc, argv);
-		if (!strcmp(argv[0], "write"))
-			return graph_write(argc, argv);
-	}
+	if (!strcmp(argv[0], "verify"))
+		return graph_verify(argc, argv);
+	else if (argc && !strcmp(argv[0], "write"))
+		return graph_write(argc, argv);
 
+usage:
 	usage_with_options(builtin_commit_graph_usage,
 			   builtin_commit_graph_options);
 }