message extraction does not handle errors

[Geal]

I've seen some cases like this one: https://github.com/wyyerd/pulsar-rs/blob/master/src/connection.rs#L233

where we're waiting for the success response but an error response can come. See both options for CommandSend here: https://github.com/wyyerd/pulsar-rs/blob/master/PulsarApi.proto#L877-L878