private void scratch() throws java.io.IOException {
        if (!possibleFlush() && current.position() != 0) {
            current.flip();
            add(current);
            current = ByteBuffer.allocate(BUFFERSIZE);
        }
    }
Data store for AbstractByteWriter. Tested in unit tests for ByteWriter.

@author Steinar Knutsen
vespajlib/src/main/java/com/yahoo/io/BufferChain.java