It doesn't matter much if the handle is invalid, as the PutWorkItem call will just fail.
But the handle could in theory be reallocated for a different queue. Also, if queues are supposed to be refcounted, it looks quite wrong that a thread which doesn't have a reference to a handle is accessing it; that's the sort of thing that generally causes memory errors.
It might be the case that our current implementation is preventing any of this from being a problem in practice, but it's fragile and unidiomatic, and it is rather confusing to anyone reading the code; it looks like an error.