Fix to read data even if stdin is a stream

If, stdin is not a file, it is neither redirection file, if data is streaming,
It is erro such as:

```bash
$ convert input.png jpeg:- | ./jpeg-recompress - output.jpg
Only able to read 123824 bytes!
```

This PR will fix to read the input data in such cases.


Actually, disregard that. It seems to break on Ubuntu for me, so I've added it back in again.