|Subject:||Crashes when "host" argument is undef|
In the original AnyEvent::Handle, the `tcp_server` function binds to all IP addresses when the host argument is undef. This is sensible behavior. However, when the host argument (the first element of the `bind` array) to AnyEvent::Handle::UDP is undef, it crashes and takes the process with it. It should be changed to bind all addresses (ideally both '0.0.0.0' and '::') instead.