SQSMessageConsumerPrefetch keeps fetching messages after stop

1. We have TestA: this test sends the message in the `testAQueue`, and checks some response after it was processed
2. We have TestB: this test invokes http endpoint and waits for the message in the `testAQueue`

When we run TestA, we start JMS Listener for the `testAQueue`. After the test, we stop the listener
When we run TestB, sometimes message in the `testAQueue` does not appear immediately, but appears after `WAIT_TIME_SECONDS`
Both tests should run one after another.

After some debugging, it appears that `SQSMessageConsumerPrefetch` tries to fetch the message even when `running = false`
I've put a non-suspending breakpoint here: https://github.com/awslabs/amazon-sqs-java-messaging-lib/blob/master/src/main/java/com/amazon/sqs/javamessaging/SQSMessageConsumerPrefetch.java#L261
to print the state of the `running` flag. When the error I've described is hit, the flag `running` is in `false` state.

Start in src/main/java/com/amazon/sqs/javamessaging/SQSMessageConsumerPrefetch.java at the breakpoint around line 261, then reproduce the sequential TestA/TestB scenario described in the issue. Trace the listener stop and the running flag; done means stopping the listener no longer causes a message fetch, so the following test can receive its message without the delay.

Written by the indexing model from the issue text.