Fix `Vector` class

This is generated when compiling `haxe.ds.Vector`:
```cpp
this1->size() = (uint32_t)(10);
```

```haxe
package;



function main() {
    var vec = new haxe.ds.Vector(10);

    for (i in 0...vec.length) {
      vec[i] = i;
    }

    trace(vec[0]); // 0
    trace(vec[5]); // 5
    trace(vec[9]); // 9
}
```