void overwriteLongAtOffset(final int offset, final long value) {
        longBuffer.rewind();
        longBuffer.put(value);
        System.arraycopy(longRawBuffer, 0, this.getRawBuffer(), offset, BlockGZIPConstants.LONG_BYTES);
    }
Helper to over write a long The buffer must be as big as the offset.

@param offset to use
@param value  long to write
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/BlockByteArrayOutputStream.java