Investigate possible bug with timeout

There might be a bug with `timeout()` calling the `onTimeout` callback even though the property delivers a value.

``` dart
property.where((beOpt) => beOpt is Some).timeout(timeout, onTimeout: (_) {
  _log.finest('timed out after $timeout waiting for Some property value');
  return const None();
}).first.then((beOpt) {
 // do something
});
```
