INT-3573: Fix `EEvalSplitter` for `Iterator`

JIRA: https://jira.spring.io/browse/INT-3573

Fix `seen` `Queue` `NPE` for `(S)FtpInboundRemoteFileSystemSynchronizerTests`:
https://build.spring.io/browse/INT-B41-JOB1-164/test/case/155357717

**Cherry-pick to 4.0.x**
INT-3560: Fix DelayHandler for Duplicate Messages

JIRA: https://jira.spring.io/browse/INT-3560

Previously, messages arriving at the delayer before the
the context was initialized would be emitted twice after
the context `refresh()` or a JMX invocation of `reschedulePersistedMessages()`.

When using a `SimpleMessageStore`, the "re" scheduled
message from the context refreshed event (or a JMX invocation)
would be re-handled unconditionally.

This was due to incorrect logic to handle the way the `SMS` stores messages.

Change the logic to correctly handle (ignore)  duplicate scheduled
releases when using `SMS`.
INT-3576: Fix NPE in the `RedisAvailableTests`

JIRA: https://jira.spring.io/browse/INT-3576