Change negated age timestamp to be open-ended

Instead of passing MAX_VALUE to the index, pass null.
Null is a special value for largest value in the field.

Change-Id: Id464a06248ed111904818bf6f325cecde5ede1b9

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneChangeIndex.java

@@ -337,7 +337,7 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
       return NumericRangeQuery.newIntRange(
           r.getField().getName(),
           toIndexTime(r.getMaxTimestamp()),
-          Integer.MAX_VALUE,
+          null,
           true, true);
     }
     throw new QueryParseException("cannot negate: " + r);