Wingman: empty case code lens spurious appears for genuine empty-cases

```haskell
absurd :: Void -> a
absurd v = case v of
```

has a `Case split (Void)` code action, but it shouldn't because there are actually no constructors here that can typecheck. This is an extremely easy fix, to just check `not . null . tacticsGetDataCons` before emitting the code lens.