INT-3478:SftpPersistentAcceptOnceFileListFilter use getFilename

JIRA: https://jira.spring.io/browse/INT-3478
Good. 
Should we add a test case on the matter?
Or: how does it affect existing tests?
Can I check somehow that it is OK?
Can we somehow adapt Gary's comment in JIRA to the test-case?

Sorry, that I'm producing so much question, but it should be at least comment on commit, why there is no test for such a change.

Thanks