[JSC] yield* in sync generators must reuse iterator result object received from inner iterator

[GSkachkov]

```
var O = { [Symbol.iterator]() { return this; }, next() { return { floof: 1, done: false, value: 1 }; } }; 
function* g() { yield* O; } 
let it = g(); 
it.next(); // { done: false, value: 1; }, BUT should be { floof: 1, done: false, value: 1 }, same object returned from .next();
```

[Radar WebKit Bug Importer]

<rdar://problem/113884618>