Add assertion

Author: jasontedor

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java

@@ -349,6 +349,7 @@ private IndexMetaData(Index index, long version, long mappingVersion, long[] pri
 
         this.index = index;
         this.version = version;
+        assert mappingVersion >= 0 : mappingVersion;
         this.mappingVersion = mappingVersion;
         this.primaryTerms = primaryTerms;
         assert primaryTerms.length == numberOfShards;