Corrected field initialization for automatic indexing events

--HG--
branch : dev

src/Orchard.Web/Modules/Orchard.Indexing/Handlers/CreateIndexingTaskHandler.cs

@@ -19,6 +19,7 @@ namespace Orchard.Indexing.Handlers {
             IEnumerable<IIndexNotifierHandler> indexNotifierHandlers
             ) {
             _indexingTaskManager = indexingTaskManager;
+            _indexNotifierHandlers = indexNotifierHandlers;
 
             OnPublishing<ContentPart<CommonPartRecord>>(CreateIndexingTask);
             OnRemoved<ContentPart<CommonPartRecord>>(RemoveIndexingTask);