q tree model bindings: add missing stamp

The stamp is used to mark the GtkTreeIter as valid.

Issue: #80698
Change-Id: I1f0d9ad0c655682573a948184287342967e35664
diff --git a/src/models/gtkqtreemodel.cpp b/src/models/gtkqtreemodel.cpp
index 38ac91f..0a18e77 100644
--- a/src/models/gtkqtreemodel.cpp
+++ b/src/models/gtkqtreemodel.cpp
@@ -309,6 +309,7 @@
             for( int row = sourceStart; row <= sourceEnd; row++) {
                 QModelIndex idx = proxy_model->index(row, 0, sourceParent);
                 GtkTreeIter iter_old;
+                iter_old.stamp = stamp;
                 qmodelindex_to_iter(idx, &iter_old);
                 GtkTreePath *path_old = gtk_q_tree_model_get_path(GTK_TREE_MODEL(retval), &iter_old);
                 gtk_tree_model_row_deleted(GTK_TREE_MODEL(retval), path_old);