INT 21 - Attachmate Extra - GET HOST WINDOW CURSOR POSITION
        AH = A5h
        AL = window number (1-4=host B-E)
Return: BX = cursor position (80 * row + column, where 0:0 is upper left)
Note:   if the host window is configured with the Extended Attribute (EAB)
          feature, multiply the cursor position by 2 to obtain the byte offset
          into the display buffer