Don't crash for clients without a last will

References #74

deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl

@@ -601,12 +601,16 @@ ensure_queue(Qos, #proc_state{ channels      = {Channel, _},
             {Q, PState}
     end.
 
+send_will(PState = #proc_state{will_msg = undefined}) ->
+    PState;
+
 send_will(PState = #proc_state{will_msg = WillMsg = #mqtt_msg{retain = Retain, topic = Topic}, retainer_pid = RPid}) ->
     amqp_pub(WillMsg, PState),
     case Retain of
         false -> ok;
         true  -> hand_off_to_retainer(RPid, Topic, WillMsg)
-    end.
+    end,
+    PState.
 
 amqp_pub(undefined, PState) ->
     PState;