DistributedEntryRetriever throws NPE if iterator is closed before processing all responses

DistributedEntryRetriever itrerator needs to ignore responses from nodes if a iterator is closed early or if a rehash occurs causing some redundant requests to be sent.

This was covered in a previous version but refactoring lost it somehow and instead the code is using variables that cannot be null.

} else if (log.isTraceEnabled()) {
         log.tracef("Ignoring values as identifier %s was marked as complete", identifier);
      }