INT 49 - MAGic v1.16+ - GET SIZE OF MAGNIFICATION WINDOW
        AX = 0007h
Return: AX = status
            0000h successful
                BX = vertical size (char rows or pixel rows)
                DX = horizontal size (char cols or 8-pixel units)
            FFFEh invalid function
            FFFFh MAGic busy, retry later
                BX,DX destroyed
        CX destroyed
BUG:    in v1.16 and v1.17, this function is not recognized as valid, but
          AX=0000h is accepted and will branch into hyperspace
SeeAlso: AX=0006h