cannot satisfy ability handler exhaustiveness check in presense of Void

[ceedubs]

Describe and demonstrate the bug

Input:

```unison
foo : '{Abort} Void -> Text
foo f = handle f () with cases
  { r } -> absurd r
  { abort -> _ } -> "aborted"
```

The above fails to compile with the error message This case would be ignored because it's already covered by the preceding case(s)

However if you remove the { r } case then it fails with:

  Pattern match doesn't cover all possible cases:
        2 | foo f = handle f () with cases
        3 |   { abort -> _ } -> "aborted"
    
  
  Patterns not matched:
   * { _ }

Environment (please complete the following information):

• ucm --version 05e2184
• OS/Architecture: x86 NixOS

Additional context

This was previously investigated over a year ago and there are some details here.

[ceedubs]

Strangely, if you replace absurd r with a string literal, it compiles again. Perhaps if you don't reference r it infers a handler that is universal with respect to the return type, so it doesn't consider { r } to be an impossible case?