Improvements in MQTT publish processing

@@ -340,6 +340,7 @@ final class MqttClientImpl implements MqttClient {
         MqttPublishVariableHeader variableHeader = new MqttPublishVariableHeader(topic, getNewMessageId().messageId());
         MqttPublishMessage message = new MqttPublishMessage(fixedHeader, variableHeader, payload);
         MqttPendingPublish pendingPublish = new MqttPendingPublish(variableHeader.packetId(), future, payload.retain(), message, qos);
+        this.pendingPublishes.put(pendingPublish.getMessageId(), pendingPublish);
         ChannelFuture channelFuture = this.sendAndFlushPacket(message);
 
         if (channelFuture != null) {
@@ -350,9 +351,9 @@ final class MqttClientImpl implements MqttClient {
             }
         }
         if (pendingPublish.isSent() && pendingPublish.getQos() == MqttQoS.AT_MOST_ONCE) {
+            this.pendingPublishes.remove(pendingPublish.getMessageId());
             pendingPublish.getFuture().setSuccess(null); //We don't get an ACK for QOS 0
         } else if (pendingPublish.isSent()) {
-            this.pendingPublishes.put(pendingPublish.getMessageId(), pendingPublish);
             pendingPublish.startPublishRetransmissionTimer(this.eventLoop.next(), this::sendAndFlushPacket);
         }
         return future;