INT 2F - DOS 5+ - QUERY FREE HMA SPACE
        AX = 4A01h
Return: BX = number of bytes available in HMA (0000h if DOS not using HMA)
        ES:DI -> start of available HMA area (FFFFh:FFFFh if not using HMA)
Note:   called by Windows 3.1 DOSX.EXE
SeeAlso: AX=4310h,AX=4A02h

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