[Broker] Handle NPE when full key range isn't covered with active consumers (apache#11749)

(cherry picked from commit 8027ab4)

Author: lhotari

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

@@ -175,8 +175,12 @@ protected void sendMessagesToConsumers(ReadType readType, List<Entry> entries) {
         for (Entry entry : entries) {
             int stickyKeyHash = getStickyKeyHash(entry);
             Consumer c = selector.select(stickyKeyHash);
-            groupedEntries.computeIfAbsent(c, k -> new ArrayList<>()).add(entry);
-            consumerStickyKeyHashesMap.computeIfAbsent(c, k -> new HashSet<>()).add(stickyKeyHash);
+            if (c != null) {
+                groupedEntries.computeIfAbsent(c, k -> new ArrayList<>()).add(entry);
+                consumerStickyKeyHashesMap.computeIfAbsent(c, k -> new HashSet<>()).add(stickyKeyHash);
+            } else {
+                entry.release();
+            }
         }
 
         AtomicInteger keyNumbers = new AtomicInteger(groupedEntries.size());