INT 21 - Far East DOS 3.2+ - GET DOUBLE BYTE CHARACTER SET LEAD TABLE
        AX = 6300h
Return: AL = error code
            00h successful
                DS:SI -> DBCS table (see below)
                all other registers except CS:IP and SS:SP destroyed
            FFh not supported
Notes:  probably identical to AH=63h/AL=00h for DOS 2.25
        the US version of MSDOS 3.30 treats this as an unused function,
          setting AL=00h and returning immediately
        the US version of DOS 4.0+ accepts this function, but returns an empty
          list

Format of DBCS table:
Offset  Size    Description
 00h  2 BYTEs   low/high ends of a range of leading byte of double-byte chars
 02h  2 BYTEs   low/high ends of a range of leading byte of double-byte chars
        ...
  N   2 BYTEs   00h,00h end flag