Improve comparator when search sort field does not exist

[LuXugang]

Description

 public void test111() throws IOException{

    Directory dir = newDirectory();
    IndexWriterConfig iwc = new IndexWriterConfig(new MockAnalyzer(random()));
    RandomIndexWriter indexWriter = new RandomIndexWriter(random(), dir, iwc);
    Document doc;
    Random random = new Random();
    int count = 0;
    while (count++ < 100000){
      doc = new Document();
      doc.add(new SortedSetDocValuesField("sortedSet", new BytesRef("a")));
      doc.add(new StringField("name", String.valueOf(random.nextInt(1000000)), StringField.Store.YES));
      indexWriter.addDocument(doc);
    }
    indexWriter.commit();

    IndexReader reader = indexWriter.getReader();
    IndexSearcher searcher = newSearcher(reader);

    assert reader.maxDoc() == 100000;
    Query query = new MatchAllDocsQuery();
    Sort sort = new Sort(new SortedSetSortField("field no exist ", false));

    TopDocs noSearchField = searcher.search(query, 2000);
    assert noSearchField.totalHits.value == 2001;

    TopDocs hasSearchField = searcher.search(query, 2000, sort);
    // if the search sort field is not exist,  should early terminate after Top 2000 collected?
    assert hasSearchField.totalHits.value == 100000;

    indexWriter.close();
    reader.close();
    dir.close();

  }

If search sort field does not exist, should we early terminate collection after TopN collected?

[serhiy-bzhezytskyy]

I put up a PR for this: #16411.

Root cause: when the sort field is missing from the whole index, every doc ties on the missing value, so with no tie-breaker the remaining docs are non-competitive once the top-N queue is full — but TermOrdValComparator didn't recognize that and scanned every document. The PR mirrors the existing singleSort competitive-iterator recognition to the minOrd path (gated on bottomValue == null) so it early-terminates. Results are unchanged; it's purely an optimization, with a regression test in TestSortOptimization.

Happy to adjust the approach if there's a preferred way to handle it.