INT 62 u - FGDRIVER v3.03 - "FG_IMAGESIZ" - DETERMINE IMAGE STORAGE REQUIREMENT
        AX = 004Bh
        BX = image width in pixels
        CX = image height in pixels
Note:   For FGDRIVER v1.10, this function was "FG_REVIMAGE" (see AX=0085h);
          "FG_IMAGESIZ" was AX=0062h
Return: DX:AX = size in bytes of mode-specific bitmap for current video mode
SeeAlso: AX=0031h,AX=007Dh

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