INT 2F - Communicating Applications Specification - OPEN FILE
        AX = CB07h
        BX = event handle from find (AL=05h,06h) or submit task (AL=01h)
        CX = receive file number (ignored for task queue and log queue)
            0000h  open receive control file
            N      open Nth received data file
        DL = queue
            00h task queue
            01h receive queue control file or received file, as given by CX
            02h log queue
            03h group file in task queue (v1.2+)
            04h group file in log queue (v1.2+)
Return: AX = 0000h successful
            BX = DOS file handle for requested file
           < 0     error code (see AX=CB01h)
Note:   the returned file handle has been opened in read-only mode and should
          be closed with INT 21/AH=3Eh after use
SeeAlso: AX=CB05h,AX=CB14h