@Override
    public void mark(int readlimit) {
        if (segmentInputStream != null) {
            segmentInputStream.mark(readlimit);
        }
    }
Wrapper for a nested input stream.
<p>
You must call getNextEntry and closeEntry like the ZIP API.
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/RANestedInputStream.java