[bugfix] Don't produce a warning that we expected zero listeners when there are zero listeners

Author: adamretter

exist-core/src/main/java/org/exist/storage/NotificationService.java

@@ -104,7 +104,10 @@ public synchronized void debug() {
     @Override
     public void shutdown() {
         synchronized (this) {
-            LOG.warn("Expected 0 listeners at shutdown, but {} listeners are still registered", listeners.size());
+            final int remainingListeners = listeners.size();
+            if (remainingListeners > 0) {
+                LOG.warn("Expected 0 listeners at shutdown, but {} listeners are still registered", remainingListeners);
+            }
         }
         BrokerPoolService.super.shutdown();
     }