Issue 717:  Fix integer overflow when computing location of volume descriptor

The multiplication here defaulted to 'int' but calculations
of file positions should always use int64_t.  A simple cast
suffices to fix this since the base location is always 32 bits
for ISO, so multiplying by the sector size will never overflow
a 64-bit integer.
isBootRecord(struct iso9660 *iso9660, const unsigned char *h)
{
	(void)iso9660; /* UNUSED */

	/* Type of the Volume Descriptor Boot Record must be 0. */
	if (h[0] != 0)
		return (0);

	/* Volume Descriptor Version must be 1. */
	if (h[6] != 1)
		return (0);

	return (1);
}

isBootRecord(struct iso9660 *iso9660, const unsigned char *h)
{
	(void)iso9660; /* UNUSED */

	/* Type of the Volume Descriptor Boot Record must be 0. */
	if (h[0] != 0)
		return (0);

	/* Volume Descriptor Version must be 1. */
	if (h[6] != 1)
		return (0);

	return (1);
}
