stack underflow with generator

```javascript
function* x() {
    for (var e of yield []);
}

var g = x();
g.next();      
g.return("test"); 
```

The root cause of this issue is that yield is being incorrectly identified as being inside a for...of statement, but in reality, the yield hasn't actually entered the for...of loop yet. As a result, an incorrect nip_catch was generated. Could you help look into fixing this?