Records are not acknowledged or the offsets are not updated in single.threaded mode

[subkanthi]

In addition to markProcessed , the call to markBatchFinished has to added in single.threaded mode.

                if(record.isLastRecordInBatch()) {
                    try {
                        record.getCommitter().markBatchFinished();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }