@Override
    protected boolean processFirstDataBlock() throws IOException {
      seeker.rewind();
      return true;
    }
Updates the current block to be the given {@link HFileBlock}. Seeks to the the first
key/value pair.
@param newBlock the block to make current, and read by {@link HFileReaderImpl#readBlock},
                it's a totally new block with new allocated {@link ByteBuff}, so if no
                further reference to this block, we should release it carefully.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java