Fix breaking change of the deprecated constructor of PersistentMessag…

…eExpiryMonitor

### Motivation

apache#20781 adds a new constructor to
`PersistentMessageExpiryMonitor` and initialize the old constructor with

```java
this.topic = subscription.topic;
```

NPE will happen when `subscription` is null. However, it's allowed to
pass a null `subscription` for test because methods like
`findEntryFailed` don't depend on the `topic` field.

### Modifications

Add the null check and mark the old constructor as deprecated.

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentMessageExpiryMonitor.java

@@ -72,10 +72,11 @@ public PersistentMessageExpiryMonitor(PersistentTopic topic, String subscription
                 && this.cursor.getManagedLedger().getConfig().isAutoSkipNonRecoverableData();
     }
 
+    @Deprecated
     public PersistentMessageExpiryMonitor(String topicName, String subscriptionName, ManagedCursor cursor,
                                           PersistentSubscription subscription) {
         this.topicName = topicName;
-        this.topic = subscription.topic;
+        this.topic = (subscription == null) ? null : (PersistentTopic) subscription.getTopic();
         this.cursor = cursor;
         this.subName = subscriptionName;
         this.subscription = subscription;