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.
archive_read_format_iso9660_read_data_skip(struct archive_read *a)
{
	/* Because read_next_header always does an explicit skip
	 * to the next entry, we don't need to do anything here. */
	(void)a; /* UNUSED */
	return (ARCHIVE_OK);
}

archive_read_format_iso9660_read_data_skip(struct archive_read *a)
{
	/* Because read_next_header always does an explicit skip
	 * to the next entry, we don't need to do anything here. */
	(void)a; /* UNUSED */
	return (ARCHIVE_OK);
}
