Append - Set return found name state

        Entry:
          AX = B711h

        Note: If the next INT 21h call (and ONLY the next) is function 3Dh,
              43h, or 6Ch, the fully qualified filename is written over top
              of the filename passed to the INT 21h call.
              The application must provide a sufficiently large buffer.
              This state is reset after next INT 21h call processed by
              APPEND.