Read date from the stream.

        The timezone is ignored as the date is always in UTC.

def readDate(self):
        """
        Read date from the stream.

        The timezone is ignored as the date is always in UTC.
        """
        ref = self.readInteger(False)

        if ref & REFERENCE_BIT == 0:
            return self.context.getObject(ref >> 1)

        ms = self.stream.read_double()
        result = util.get_datetime(ms / 1000.0)

        if self.timezone_offset is not None:
            result += self.timezone_offset

        self.context.addObject(result)

        return result