`dischargeCekValue` doesn't handle open terms correctly

`dischargeCekValue` has the following code:

```haskell
-- var is free, leave it alone
(Var () named)
```

which means that

`(\0 \0 var 2) (delay (var 1))`

evaluates to

`[1 :-> delay (var 1)] (\0 var 2)`

which then discharges to

`\0 delay (var 1)`

which is variable capture.