Fail fast when using bus.Defer in OneWayClientMode
- When the bus is in OneWayClientMode, Defer does not work because there
  is no way for the timeout service to return the message, specifically
  no return address gets set in the headers. This commit ensures the call
  to Defer fails, making it easier for the user to discover his error.
TimeoutRequestHandler, fail if no return address is set.
- Without this commit, the handler will happily try to insert the timeout
  into underlying storage with a null value for ReplyTo, which then fails.
  Fail early to ensure the thrown exception describes the actual problem.