INT 62 u - FGDRIVER v3.03 - "FG_PCXHEAD" - GET PCX FILE HEADER
        AX = 0073h
        ES:BX -> variable pointer record (see below)
Return: AX = status
            0000h successful
            FFFEh not a PCX file
            FFFFh file does not exist
Note:   For FGDRIVER v1.10, this function was "FG_SETNUM" (see AX=0094h);
           "FG_PCXHEAD" did not exist yet
SeeAlso: AX=0074h,AX=009Ah

Format of variable pointer record:
Offset  Size    Description
 00h    WORD    segment of ASCIZ filename
 02h    WORD    offset of ASCIZ filename
 04h    WORD    segment of 128-byte buffer for PCX header
 06h    WORD    offset of 128-byte buffer for PCX header

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