v1.11.1

Avoid trying to checkpoint _and_ load up messages in the same invocation

Based on observations seen in a real-world scenario it is possible for
the checkpoint to exhaust memory after it has already been filled with
messages that sqs-ingest is trying to buffer from SQS.

This is not foolproof with concurrent executions but it's an attempt
which is better than nothing :smile:

Signed-off-by: R. Tyler Croy <rtyler@buoyantdata.com>