This commit aligns the XML and Java based validations.
When using XML to configure a chunk oriented step both an ItemReader and
ItemWriter are requied. However when using Java based configuration the
ItemWriter is optional if an ItemProcessor is present.
Having no ItemWriter and only an ItemProcessor lead to strange results
in one of our batch jobs, which was accidentily configured without an
ItemProcessor.
Related: BATCH-1520
Fixes: BATCH-2624
3ccc4ff430