GH-1145: Backport NPE Fix

Resolves #1145

**cherry-pick to 2.0.x, 1.3.x**

Author: garyrussell

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

@@ -630,7 +630,10 @@ else if (KafkaMessageListenerContainer.this.getContainerProperties().isSyncCommi
 			};
 		}
 
-		private void seekPartitions(Collection<TopicPartition> partitions, boolean idle) {
+		private void seekPartitions(@Nullable Collection<TopicPartition> partitions, boolean idle) {
+			if (partitions == null) {
+				return;
+			}
 			Map<TopicPartition, Long> current = new HashMap<>();
 			for (TopicPartition topicPartition : partitions) {
 				current.put(topicPartition, ListenerConsumer.this.consumer.position(topicPartition));