DOS Fn 15H: Write Sequential File via FCB

                                                         Compatibility: 1.0+ 
 Expects: AH    15H
          DS:DX address of an opened FCB
 Returns: AL    0 if the write was successful
                1 if "disk full" error and no data was written
                2 if DTA+ FCB recSize would overrun a segment (no write)
    Info: Writes recSize bytes from the DTA to the file address specified
          by curBlk and curRec (as specified in the FCB).  Then increments
          the block-and-record file address.

          Be sure to set CurRec to 0 before starting sequential file
          operations, since DOS Fn 0fH Open FCB does not initialize it.

   Notes: ■ DOS buffers data until a full sector can be written at one time
            (or until the file is closed).

See Also: Fn 1aH (set DTA)
          Fn 40h (write to handle)
          FCB File I/O
          Handle-Oriented File I/O
          DOS Functions