INT 21,46 - Force Duplicate File Handle

AH = 46h

BX = existing file handle

CX = second file handle

on return:

AX = error code if CF set (see ~DOS ERROR CODES~)

- if file handle in CX is currently open, current file

identified by CX is closed and the handle in BX is

dupped and placed in CX

- after duping file handles move together through file

- similar to ~INT 21,45~