Calling Kinesis connector close method before subtask starts running results in NPE

When a Flink application is stopped before a Kinesis connector subtask has been started, the following exception is thrown:

java.lang.NullPointerException
at org.apache.flink.streaming.connectors.kinesis.FlinkKinesisConsumer.close(FlinkKinesisConsumer.java:421)
...

This appears to be related to the fact that fetcher creation may not occur by the time it is referenced when the consumer is closed.

A suggested fix is to make the close() method null safe as it has been in the cancel() method.