GH-1134: Fix stop(Runnable) usage

Fixes #1134

We always have to call `callback` in the `stop(Runnable)` implementation
independently of the component state

**Cherry-pick until 1.1.x to support Spring Boot 1.5.x**

spring-kafka/src/main/java/org/springframework/kafka/config/KafkaListenerEndpointRegistry.java

@@ -248,16 +248,21 @@ public void stop() {
 
 	@Override
 	public void stop(Runnable callback) {
-		Collection<MessageListenerContainer> listenerContainers = getListenerContainers();
-		AggregatingCallback aggregatingCallback = new AggregatingCallback(listenerContainers.size(), callback);
-		for (MessageListenerContainer listenerContainer : listenerContainers) {
-			if (listenerContainer.isRunning()) {
-				listenerContainer.stop(aggregatingCallback);
-			}
-			else {
-				aggregatingCallback.run();
+		Collection<MessageListenerContainer> listenerContainersToStop = getListenerContainers();
+		if (listenerContainersToStop.size() > 0) {
+			AggregatingCallback aggregatingCallback = new AggregatingCallback(listenerContainersToStop.size(), callback);
+			for (MessageListenerContainer listenerContainer : listenerContainersToStop) {
+				if (listenerContainer.isRunning()) {
+					listenerContainer.stop(aggregatingCallback);
+				}
+				else {
+					aggregatingCallback.run();
+				}
 			}
 		}
+		else {
+			callback.run();
+		}
 	}
 
 	@Override

spring-kafka/src/main/java/org/springframework/kafka/listener/AbstractMessageListenerContainer.java

@@ -264,6 +264,9 @@ public void stop(Runnable callback) {
 			if (isRunning()) {
 				doStop(callback);
 			}
+			else {
+				callback.run();
+			}
 		}
 	}