spring-projectsGH-3695: Fix MessagingMessageListenerAdapter to not …

…ack when sync

Fixes: spring-projects#3695

Even if th `@KafkaHandler` method is `void` the `DelegatingInvocableHandler` returns an empty `InvocationResult`.
That triggers a `MessagingMessageListenerAdapter.handleResult()` logic.
On the `completableFutureResult.whenComplete()` we call `acknowledge()` which is not expected for `void` POJO methods.

* Fix `MessagingMessageListenerAdapter` to check for `isAsyncReplies()` before calling `acknowledge()`

This is a regression after spring-projects#3528

spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/MessagingMessageListenerAdapter.java

@@ -80,9 +80,9 @@
 import org.springframework.util.TypeUtils;
 
 /**
- * An abstract {@link org.springframework.kafka.listener.MessageListener} adapter
+ * An abstract {@link MessageListener} adapter
  * providing the necessary infrastructure to extract the payload of a
- * {@link org.springframework.messaging.Message}.
+ * {@link Message}.
  *
  * @param <K> the key type.
  * @param <V> the value type.
@@ -205,9 +205,9 @@ public void setMessageConverter(RecordMessageConverter messageConverter) {
 
 	/**
 	 * Return the {@link MessagingMessageConverter} for this listener,
-	 * being able to convert {@link org.springframework.messaging.Message}.
+	 * being able to convert {@link Message}.
 	 * @return the {@link MessagingMessageConverter} for this listener,
-	 * being able to convert {@link org.springframework.messaging.Message}.
+	 * being able to convert {@link Message}.
 	 */
 	protected final RecordMessageConverter getMessageConverter() {
 		return this.messageConverter;
@@ -550,7 +550,9 @@ else if (!(result instanceof CompletableFuture<?>)) {
 			try {
 				if (t == null) {
 					asyncSuccess(r, replyTopic, source, messageReturnType);
-					acknowledge(acknowledgment);
+					if (isAsyncReplies()) {
+						acknowledge(acknowledgment);
+					}
 				}
 				else {
 					Throwable cause = t instanceof CompletionException ? t.getCause() : t;