base85 debug code: Fix length byte calculation

Signed-off-by: NAndreas Gruenbacher <agruen@suse.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

base85.c

@@ -118,7 +118,7 @@ int main(int ac, char **av)
 		int len = strlen(av[2]);
 		encode_85(buf, av[2], len);
 		if (len <= 26) len = len + 'A' - 1;
-		else len = len + 'a' - 26 + 1;
+		else len = len + 'a' - 26 - 1;
 		printf("encoded: %c%s\n", len, buf);
 		return 0;
 	}