INT 31 P - DPMI 1.0+ - GET MEMORY BLOCK SIZE AND BASE
        AX = 050AH
        SI:DI = memory block handle
Return: CF clear if successful
            SI:DI = size in bytes
            BX:CX = base address
        CF set on error
            AX = error code (8023h) (see AX=0000h)
SeeAlso: AX=0504h