vsprintf: pre-calculate final string length for later use

		case FORMAT_TYPE_STR: {

			const char *save_str = va_arg(args, char *);

			size_t len;

			if ((unsigned long)save_str > (unsigned long)-PAGE_SIZE

					|| (unsigned long)save_str < PAGE_SIZE)

				save_str = "(null)";

			len = strlen(save_str);

			if (str + len + 1 < end)

				memcpy(str, save_str, len + 1);

			str += len + 1;

			len = strlen(save_str) + 1;

			if (str + len < end)

				memcpy(str, save_str, len);

			str += len;

			break;

		}