zstring.Format with 4+ count args will cause IndexOutOfRangeException

[jarekzha]

code below will cause IndexOutOfRangeException

            string text;
            using (zstring.Block())
            {
                var sign = "";
                text = zstring.Format("hello:{0}:{1}:{2}:{3}",123, "abc", sign, 3);
            }
            return text;

IndexOutOfRangeException: Index was outside the bounds of the array.
zstring.internal_format (System.String input, System.Int32 num_args) (at zstring.cs:369)
zstring.Format (System.String input, zstring arg0, zstring arg1, zstring arg2, zstring arg3) (at zstring.cs:1508)

if args count is less than 4, code will success.