Miscompilation of closure capture on JS

The following program (v1) is miscomplied on JS, whereas v2 is compiled correctly.
This likely has something to do with contification / the direct-style transform on JS as Chez-CPS seems to be correct.

```scala
def main() = {
var adders = []

each(1, 4) { x =>
println(x) // <- this line only on v1
// println(s"debug ${x.show}") // <- this line only on v2
adders = Cons(box { (y: Int) => y + x }, adders)
}

adders.foreach { adder =>
println(adder(3))
}
}
```

```sh
bash-5.3$ effekt --backend=js v1.effekt v2.effekt
1
2
3
7
7
7

debug 1
debug 2
debug 3
6
5
4

bash-5.3$ effekt --backend=llvm v1.effekt v2.effekt
1
2
3
6
5
4

debug 1
debug 2
debug 3
6
5
4

bash-5.3$ effekt --backend=chez-cps v1.effekt v2.effekt
1
2
3
6
5
4

debug 1
debug 2
debug 3
6
5
4
```