@Override
        public int read() throws IOException {
            if (bytesRead < getCurrentBlockRawGzipSize()) {
                bytesRead++;
                return getCurrentRawStreamBuffer().read();
            }
            return -1;
        }
Adaptor to create a stream over the raw buffer and ensures that we don't
read more than we are allowed to (for the gzip stream)
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/BlockGZIPInput.java