@Override
    public boolean nextInterval() {
        if (currentIntervalIndex < currentIntervals.length) {
            this.currentInterval = currentIntervals[currentIntervalIndex++];
            return true;
        }
        return false;
    }
Implementation of PostingList for regular features that store
their intervals and nothing else.

@author Magnar Nedland
@author bjorncs
predicate-search/src/main/java/com/yahoo/search/predicate/index/IntervalPostingList.java