INT 15 - DESQview v2.20+ - "GETCRIT" - GET CRITICAL NESTING COUNT
        AX = DE13h
Return: BX = number of calls to BEGINC or ENTERC (see INT 15/AX=101Bh,DE1Ch)
             without matching ENDC (see INT 15/AX=101Ch)
Note:   this API call may be made from within a hardware interrupt handler
SeeAlso: AX=101Ch,AX=DE1Bh,AX=DE1Ch