optimizer fails when using structural subtyping

```haxe
function main() {
var w = new World();
var wrapper = new Wrapper(w);
wrapper.use();
}

class World {
public function new() {}
}

abstract Wrapper({w:{}}) {
public inline function new(w:{}) this = {w: w}; // This doesn't optimize.
// public inline function new(w:T) this = {w: w}; // These do.
// public inline function new(w:{}) this = {w: cast w};

public inline function use() trace(this.w);
}
```
This generates `({ w : new World()}).w`. The commented-out `new` variants generate just `new World()`.