@Override
    public int available() throws IOException {
        if (data == null || indexInputStream == null) {
            throw new IOException("Stream closed");
        }

        if (windowPos < windowByteEnd - 1) {
            return 1;
        }

        return 0;
    }
Indicates if there are more bytes available to read. This implementation
returns 1 if there are more bytes to read or 0 if not. This method will
throw an IOException if the data and index files are closed.

@return 1 if there are bytes to read, 0 otherwise.
@throws IOException Thrown if either the data or index streams are closed.
@see java.io.InputStream#available()
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/RASegmentInputStream.java