Improve ZeroMQ Adapter Message Serilization Error Handling

[callumforrester]

The ZMQ adapter serializes messages before pushing, there are currently two major issues with this: It raises an exception when it gets an empty message (i.e. []) and said exception is swallowed, along with any other serialization errors.

[GDYendell]

Is it expected that adding an empty message to the queue would do something useful? It could handle empty messages more explicitly to allow reporting of serialization errors of messages with actual content.