INT 21 - DOS 1+ - SET RANDOM RECORD NUMBER FOR FCB
        AH = 24h
        DS:DX -> opened FCB (see AH=0Fh)
Notes:  computes the random record number corresponding to the current record
          number and record size, then stores the result in the FCB
        normally used when switching from sequential to random access
        not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=27h,AH=42h