Get Protected Mode Interrupt Vector

Returns the address of the current protected mode interrupt
handler for the specified interrupt.

Call With:

   AX     = 0204H
   BL     = interrupt number

Returns:

   Carry flag= clear (this function always succeeds)
   CX:(E)DX= selector:offset of exception handler

Notes:

o  The value returned in CX is a valid protected mode
   selector, not a real mode segment address.
o  32-bit clients will be returned a 32-bit offset in the
   EDX register.
o  DPMI hosts must make all 100H (256) interrupt vectors
   available through this function.