Refactor getOrSetCorrelationIdAndSetReplyTo method

Refactored the `getOrSetCorrelationIdAndSetReplyTo` method for improved readability and code organization. 
Merged the declaration and initialization of `correlationId` into a single line. 
Ensured the logic remains unchanged. 
No functional changes introduced.

Author: Java4ye

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/AsyncRabbitTemplate.java

@@ -87,6 +87,7 @@
  *
  * @author Gary Russell
  * @author Artem Bilan
+ * @author FengYang Su
  *
  * @since 1.6
  */
@@ -666,18 +667,14 @@ public void confirm(@NonNull CorrelationData correlationData, boolean ack, @Null
 	private String getOrSetCorrelationIdAndSetReplyTo(Message message,
 			@Nullable AsyncCorrelationData<?> correlationData) {
 
-		String correlationId;
 		MessageProperties messageProperties = message.getMessageProperties();
 		Assert.notNull(messageProperties, "the message properties cannot be null");
-		String currentCorrelationId = messageProperties.getCorrelationId();
-		if (!StringUtils.hasText(currentCorrelationId)) {
+		String correlationId = messageProperties.getCorrelationId();
+		if (!StringUtils.hasText(correlationId)) {
 			correlationId = correlationData != null ? correlationData.getId() : UUID.randomUUID().toString();
 			messageProperties.setCorrelationId(correlationId);
 			Assert.isNull(messageProperties.getReplyTo(), "'replyTo' property must be null");
 		}
-		else {
-			correlationId = currentCorrelationId;
-		}
 		messageProperties.setReplyTo(this.replyAddress);
 		return correlationId;
 	}