When _source is disabled, don't return it in realtime get fetching the document from the transaction log, closes #1509.

modules/elasticsearch/src/main/java/org/elasticsearch/index/get/ShardGetService.java

@@ -324,6 +324,11 @@ public class ShardGetService extends AbstractIndexShardComponent {
                     }
                 }
 
+                // if source is not enabled, don't return it even though we have it from the translog
+                if (sourceRequested && !docMapper.sourceMapper().enabled()) {
+                    sourceRequested = false;
+                }
+
                 return new GetResult(shardId.index().name(), type, id, get.version(), get.exists(), sourceRequested ? source.source : null, fields);
             }
         } finally {