Fix ConsumerLagCalculator#processAllGroup retry topic NPE

[drpmma]

There may cause a NPE when retryTopic is not exist
see

rocketmq/broker/src/main/java/org/apache/rocketmq/broker/metrics/ConsumerLagCalculator.java

Lines 180 to 184 in 1986c6b

	int retryTopicPerm = retryTopicConfig.getPerm() & brokerConfig.getBrokerPermission();
	if (PermName.isReadable(retryTopicPerm) || PermName.isWriteable(retryTopicPerm)) {
	consumer.accept(new ProcessGroupInfo(group, topic, true, retryTopic));
	} else {
	consumer.accept(new ProcessGroupInfo(group, topic, true, null));