DOS Fn 21H: Read Random File Record

                                                         Compatibility: 1.0+ 
 Expects: AH    21H
          DS:DX address of an opened FCB
 Returns: AL    0 if read was successful (and DTA is filled with data)
                1 if EOF was reached and no data was read
                2 if DTA + FCB RecSize would overrun a segment (no read)
                3 if EOF and a partial record was read (padded with 0s)
    Info: Sets FCB curBlk and curRec to the agree with randomRec then reads
          recSize bytes from the specified file address, placing the data
          into memory starting at the DTA.

   Notes: ■ Be sure to set recSize to the record length and randomRec in
            the FCB to the desired record number.

See Also: Fn 3fH (read file via handle)
          FCB File I/O
          Handle-Oriented File I/O
          DOS Functions