add defensive asserts for the indexInterval / skipInterval in tis/tii files

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@769294 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/lucene/index/SegmentTermEnum.java

@@ -82,6 +82,8 @@ final class SegmentTermEnum extends TermEnum implements Cloneable {
           maxSkipLevels = input.readInt();
         }
       }
+      assert indexInterval > 0: "indexInterval=" + indexInterval + " is negative; must be > 0";
+      assert skipInterval > 0: "skipInterval=" + skipInterval + " is negative; must be > 0";
     }
     if (format > TermInfosWriter.FORMAT_VERSION_UTF8_LENGTH_IN_BYTES) {
       termBuffer.setPreUTF8Strings();