SOLR-1459: add null scorer check to QueryValueSource.java too

git-svn-id: https://svn.apache.org/repos/asf/lucene/solr/trunk@818505 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/solr/search/function/QueryValueSource.java

@@ -91,6 +91,7 @@ class QueryDocValues extends DocValues {
       if (doc < lastDocRequested) {
         // out-of-order access.... reset scorer.
         scorer = weight.scorer(reader, true, false);
+        if (scorer==null) return defVal;
         scorerDoc = -1;
       }
       lastDocRequested = doc;