Guard messes up exhaustiveness check.

The following [produces](https://try.haxe.org/#dfC1F) `Unmatched patterns: Success`:

```haxe
using tink.CoreApi;

class Test {
static function main() {
switch Success({ success: true }) {
case Success(obj) if (obj.success): trace('yes!');
case Success(obj) if (!obj.success): trace('no!');
case Failure(_): trace('no!');
};
}
}
```

That's fair enough, because guards can be arbitrarily complex.

Consequently, the following should be considered non-exhaustive for the same reasons, but [it compiles just fine](https://try.haxe.org/#64b65) even though it doesn't match:

```haxe
using tink.CoreApi;

class Test {
static function main() {
switch Success({ success: true }) {
case Success({ success: false }): trace('no!');
case Success(obj) if (!obj.success): trace('no!');
case Failure(_): trace('no!');
};
}
}
```