FlowMachine should reply to malformed ZMQ messages which have a reply address

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Describe the bug At present, if you send a bad message to FlowMachine via zmq (e.g. missing a top level key), then you don't get a reply, and the sender will get hung when it tries to receive. This is fine if the zmq message is so wrong that a reply address can't be found, but an error message should be sent back if there is a reply address.

Product FlowMachine

Version master

To Reproduce Unskip integration_tests.flowmachine_server_tests.test_action_run_query.test_wrongly_formatted_zmq_message