Make Tag#parent return the tag's parent even if it is draft.

This was causing tags to be returned via the API with blank parents, even though the parent existed in draft and draft tags had been requested.

The niggle this introduces is that if one were to request only live tags and there was a live child with a draft parent, that draft parent would be included in the response.

We are currently planning to prevent live children with draft parents so this should be a non-issue.