According to the AMQP spec, a message must have a body.

amqpnetlite and Azure Service Bus support non-compliant AMQP where a
message might have no body. RabbitMQ implements the AMQP spec correctly
requiring a message body. This commit provides a nice error description
if a client wrongly sends a message without a body.

Prior to this commit, the session got terminated with the following
non-descriptive error:
```
[{mc_amqp,msg_body_encoded,
     [[],0,
      {msg_body_encoded,undefined,[],
          {'v1_0.properties',undefined,undefined,undefined,undefined,
              undefined,undefined,undefined,undefined,undefined,undefined,
              undefined,undefined,undefined},
          [],
          <<0,83,115,69>>,
          [],uninit,uninit}],
     [{file,"mc_amqp.erl"},{line,612}]},
 {mc_amqp,init,1,[{file,"mc_amqp.erl"},{line,145}]},
 {mc,init,4,[{file,"mc.erl"},{line,157}]},
 {rabbit_amqp_session,incoming_link_transfer,4,
     [{file,"rabbit_amqp_session.erl"},{line,2409}]},
 {rabbit_amqp_session,handle_frame,2,
     [{file,"rabbit_amqp_session.erl"},{line,983}]},
 {rabbit_amqp_session,handle_cast,2,
     [{file,"rabbit_amqp_session.erl"},{line,558}]},
 {gen_server,try_handle_cast,3,[{file,"gen_server.erl"},{line,2460}]},
 {gen_server,handle_msg,3,[{file,"gen_server.erl"},{line,2418}]}]
```

(Note that transfer frames without payload are allowed though.)