[Bug] reqrespactivity/reqrespquery samples have wrong assumpion about Selector.HasPending

[cretz]

Describe the bug

When I originally developed the reqrespactivity/reqrespquery code, I had a misunderstanding about HasPending() in that I improperly assumed it would return true while a future is outstanding which is not the case, it only returns true if the future is completed and just not handled.

The samples need to be updated to not exit their loop while selector.HasPending or there are unresolved futures.