remove irrelevant TODO - segmentFileName is only added if not null

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1521038 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java

@@ -804,10 +804,6 @@ public final class SegmentInfos implements Cloneable, Iterable<SegmentInfoPerCom
     if (includeSegmentsFile) {
       final String segmentFileName = getSegmentsFileName();
       if (segmentFileName != null) {
-        /*
-         * TODO: if lastGen == -1 we get might get null here it seems wrong to
-         * add null to the files set
-         */
         files.add(segmentFileName);
       }
     }