LUCENE-6329: Calling score() should be ok even if needsScores is false.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1663756 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/search/DisjunctionScorer.java

@@ -152,13 +152,16 @@ abstract class DisjunctionScorer extends Scorer {
               previous = w;
             }
           }
+        } else {
+          // since we don't need scores, let's pretend we have a single match
+          topScorers.next = null;
+        }
 
         // We need to explicitely set the list of top scorers to avoid the
         // laziness of DisjunctionScorer.score() that would take all scorers
         // positioned on the same doc as the top of the pq, including
         // non-matching scorers
         DisjunctionScorer.this.topScorers = topScorers;
-        }
         return true;
       }
     };