fetch-pack.c: show correct command name that fails

When --shallow-file is added to the command line, it has to be
before the subcommand name, the first argument won't be the command
name any more. Stop assuming that and keep track of the command name
explicitly.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fetch-pack.c

@@ -688,7 +688,7 @@ static int get_pack(struct fetch_pack_args *args,
 	const char *argv[22];
 	char keep_arg[256];
 	char hdr_arg[256];
-	const char **av;
+	const char **av, *cmd_name;
 	int do_keep = args->keep_pack;
 	struct child_process cmd;
 
@@ -734,7 +734,7 @@ static int get_pack(struct fetch_pack_args *args,
 	if (do_keep) {
 		if (pack_lockfile)
 			cmd.out = -1;
-		*av++ = "index-pack";
+		*av++ = cmd_name = "index-pack";
 		*av++ = "--stdin";
 		if (!args->quiet && !args->no_progress)
 			*av++ = "-v";
@@ -749,7 +749,7 @@ static int get_pack(struct fetch_pack_args *args,
 		}
 	}
 	else {
-		*av++ = "unpack-objects";
+		*av++ = cmd_name = "unpack-objects";
 		if (args->quiet || args->no_progress)
 			*av++ = "-q";
 	}
@@ -766,14 +766,14 @@ static int get_pack(struct fetch_pack_args *args,
 	cmd.in = demux.out;
 	cmd.git_cmd = 1;
 	if (start_command(&cmd))
-		die("fetch-pack: unable to fork off %s", argv[0]);
+		die("fetch-pack: unable to fork off %s", cmd_name);
 	if (do_keep && pack_lockfile) {
 		*pack_lockfile = index_pack_lockfile(cmd.out);
 		close(cmd.out);
 	}
 
 	if (finish_command(&cmd))
-		die("%s failed", argv[0]);
+		die("%s failed", cmd_name);
 	if (use_sideband && finish_async(&demux))
 		die("error in sideband demultiplexer");
 	return 0;