Method prepend_zero

src/common/buffer.cc:1482–1489

  }

  void buffer::list::prepend_zero(unsigned len)
  {
    auto bp = ptr_node::create(len);
    bp->zero(false);
    _len += len;
    _num += 1;
    _buffers.push_front(*bp.release());
  }
  
  void buffer::list::append_zero2(unsigned len)
  {