DOS Fn 4406H: IOCTL Query Handle Input Status

                                                         Compatibility: 2.0+ 
 Expects: AX    4406H
          BX    file handle  (device or disk file)
 Returns: AX    error code  if CF is set to CY
          AL    input status code (if no error)
                00H: End of file or device not ready
                ffH: not EOF     or device ready
    Info: This function checks to see if a device or file is ready for
          input; i.e, has data waiting to be read.

          If the handle is a disk file:
            AL=00H file pointer has reached the end of file
            AL=ffH file pointer is at EOF (next read will return 0 bytes)

          If the handle is a device:
            AL=00H the device is not ready (no input available)
            AL=ffH the device is ready (input is available)

   Notes: ■ This fn makes for a simple way to determine EOF or to see if a
            device, such as a COM port, has any input to be read.

See Also: Fn 44H (IOCTL)
          Fn 4407H (Query Handle Output Status)
          Handle-Oriented File I/O
          DOS Functions