[asl] Fix the non-determinstic ASL primitive `somebool`

[maranget]

Before, the evaluation of the somebool primitive by "ASLSem" was yielding no candidate, because of some unsolved equations. Now, we have two candidates, as expected.

As an example the following litmus test now yields two candidates:

ASL non-deterministic

{ }

// Non deterministically returns 1 or 2
func g() => integer
begin
  let b = SomeBoolean();
  if b then
    return 1;
  end
  return 2;
end

func main() => integer
begin
  let z = g();
  return 0;
end

locations [0:main.0.z;]

[maranget]

Merged, as being a (small) bug fix.