SeekableByteChannel not seekable?

[Florian Weimer]

* Simone Bordet:

> Is that expected behavior? Seems strange that we get a
> SeekableByteChannel that does not support seek - understandable given
> the zipfs but still weird.
>
> Maybe just needs explicit documentation?

I think that in practice, FileChannel#position(long) has always been an
optional operation because it does not work on non-regular files.  This
isn't specific to zipfs, it can happen with regular file system paths as
well (if they refer to character devices or FIFOs, for example).

Thanks,
Florian