Internal method.
        Reads a double word (4 bytes) from a buffer.

def GetDWORD(self, buff, idx=0):
        '''Internal method.
        Reads a double word (4 bytes) from a buffer.
        '''
        result = buff[idx] + (buff[idx+1] << 8) + (buff[idx+2] << 16) + \
            (buff[idx+3] << 24)

        if result == 0xFFFFFFFF:
            result = 0

        return result