public boolean hasVisitedAnyBuckets() {
        return ((currentStatistics != null) && (currentStatistics.getBucketsVisited() > 0));
    }
Returns true iff the statistics reported by the visiting session indicates at least one
bucket has been completely visited.

Not thread safe, so should only be called on a quiescent session after waitUntilDone
has completed successfully.
documentapi/src/main/java/com/yahoo/documentapi/VisitorControlHandler.java