New elements panel : fix crash at drag and drop due to a wrong use of QAbstractItemModel

git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@4353 bfdf4180-ca20-0410-9c96-a3a8aa849046

sources/ElementsCollection/fileelementcollectionitem.h

@@ -30,6 +30,8 @@
  */
 class FileElementCollectionItem : public ElementCollectionItem
 {
+		Q_OBJECT
+
     public:
 		FileElementCollectionItem(ElementCollectionItem *parent = nullptr);
         ~FileElementCollectionItem();