SIGSEGV when reading object before write

```js
'use strict';
const ref = require("./build/Release/binding.node");

const buf = Buffer.alloc(64, 1);
ref.readObject(buf, 0);
```

leads to

```
segmentation fault (core dumped)  node repro.js
```

The problem is that the buffer contents are interpreted as references to object heaps before writing any reference to an object into the buffer.