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**