Handle invalid argc gently

describe, git: Handle argc==0 case the same way as argc==1.
merge-tree: Refuse excessive arguments.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

describe.c

@@ -163,7 +163,7 @@ int main(int argc, char **argv)
 
 	setup_git_directory();
 
-	if (i == argc)
+	if (argc <= i)
 		describe("HEAD", 1);
 	else
 		while (i < argc) {

git.c

@@ -294,7 +294,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 
 int main(int argc, const char **argv, char **envp)
 {
-	const char *cmd = argv[0];
+	const char *cmd = argv[0] ? argv[0] : "git-help";
 	char *slash = strrchr(cmd, '/');
 	const char *exec_path = NULL;
 	int done_alias = 0;

merge-tree.c

@@ -337,7 +337,7 @@ int main(int argc, char **argv)
 	struct tree_desc t[3];
 	void *buf1, *buf2, *buf3;
 
-	if (argc < 4)
+	if (argc != 4)
 		usage(merge_tree_usage);
 
 	setup_git_directory();