Revert Incorrect MessagingTemplate Change

The change to "optimize" the template by not rebuilding the reply
message when the original header channels was null was incorrect.

We need to null out those headers if they were originally null.

Issue: SPR-15991

spring-messaging/src/main/java/org/springframework/messaging/core/GenericMessagingTemplate.java

@@ -230,7 +230,7 @@ public class GenericMessagingTemplate extends AbstractDestinationResolvingMessag
 		}
 
 		Message<?> replyMessage = this.doReceive(tempReplyChannel, receiveTimeout);
-		if (replyMessage != null && (originalReplyChannelHeader!= null || originalErrorChannelHeader != null)) {
+		if (replyMessage != null) {
 			replyMessage = MessageBuilder.fromMessage(replyMessage)
 					.setHeader(MessageHeaders.REPLY_CHANNEL, originalReplyChannelHeader)
 					.setHeader(MessageHeaders.ERROR_CHANNEL, originalErrorChannelHeader)