[fix] Avoid NPE when closing an uninitialized SameAuthParamsLookupAutoClusterFailover (apache#23911)

(cherry picked from commit 12b0579)
(cherry picked from commit c0ee989)

Author: merlimat

pulsar-client/src/main/java/org/apache/pulsar/client/impl/PulsarClientImpl.java

@@ -253,6 +253,9 @@ private PulsarClientImpl(ClientConfigurationData conf, EventLoopGroup eventLoopG
                     this::reduceConsumerReceiverQueueSize);
             state.set(State.Open);
         } catch (Throwable t) {
+            // Log the exception first, or it could be missed if there are any subsequent exceptions in the
+            // shutdown sequence
+            log.error("Failed to create Pulsar client instance.", t);
             shutdown();
             shutdownEventLoopGroup(eventLoopGroupReference);
             closeCnxPool(connectionPoolReference);

pulsar-client/src/main/java/org/apache/pulsar/client/impl/SameAuthParamsLookupAutoClusterFailover.java

@@ -107,11 +107,21 @@ public String getServiceUrl() {
 
     @Override
     public void close() throws Exception {
+        if (closed) {
+            return;
+        }
+
         log.info("Closing service url provider. Current pulsar service: [{}] {}", currentPulsarServiceIndex,
                 pulsarServiceUrlArray[currentPulsarServiceIndex]);
+        if (scheduledCheckTask != null) {
+            scheduledCheckTask.cancel(false);
+        }
+
+        if (executor != null) {
+            executor.shutdownNow();
+        }
+
         closed = true;
-        scheduledCheckTask.cancel(false);
-        executor.shutdownNow();
     }
 
     private int firstHealthyPulsarService() {