Segmentation fault with cyclic imports 

To reproduce create two files `a.mjs` and `b.mjs`  and run `qjs a.mjs`.

a.mjs:
```javascript
import { fb } from "./b.mjs";
export { fb };
```

b.mjs:
```javascript
import * as $a from "a.mjs";
export function fb() {};
```

There is no crash if `export { fb };` is removed from `a.mjs` or the import in `b.mjs` is changed to `import {} from "a.mjs";`.