Get Descriptor

Copies the local descriptor table (LDT) entry for the
specified selector into an 8-byte buffer.

Call With:

   AX     = 000BH
   BX     = selector
   ES:(E)DI= selector:offset of 8-byte buffer

Returns:

   if function successful
   Carry flag= clear

   and buffer pointed to by ES:(E)DI contains descriptor
   if function unsuccessful
   Carry flag= set
   AX     = error code
           8022H   invalid selector

Notes:

o  32-bit programs must use ES:EDI to point to the buffer.
   16-bit programs should use ES:DI.
o  Refer to the rules for descriptor usage in Appendix D.