Empty signals does not implement `Deref`, `AsRef`, etc.

The implementation of Deref and AsRef etc. for signals is behind a branch that checks if the signal is empty. Proxy.rs line 762. I'm looking at the code for another reason, mostly just trying to understand it currently, but I'm guessing this is an oversight? I tried to create a simple proxy with an empty signal just to test, and indeed it does not implement the normal traits. I can create a PR for this is wanted 😄.