Issue in untagged variants with both an object and an array.

This is OK:
```res
  type t = | Array(array<int>) | Record({x:int})
```

But this is wrong:
```res
@unboxed
type t = Record({x: int}) | Array(array<int>)

let classify = v =>
  switch v {
  | Record({x}) => x
  | Array(a) => a[0]
  }
```

```js
function classify(v) {
  if (typeof v === "object") {
    return v.x;
  } else {
    return Caml_array.get(v, 0);
  }
}
```
