Do not set cursor on not realized TreeView

issue11596
review443421003
(grafted from a999fa1af2f4a523ba9d5610a5fe5fd75bd97526)

--HG--
branch : 6.0

tryton/gui/window/view_form/view/list.py

@@ -1142,7 +1142,7 @@ class ViewTree(View):
     def set_cursor(self, new=False, reset_view=True):
         self.treeview.grab_focus()
         model = self.treeview.get_model()
-        if self.record and model:
+        if self.record and model and self.treeview.get_realized():
             path = self.record.get_index_path(model.group)
             if model.get_flags() & Gtk.TreeModelFlags.LIST_ONLY:
                 path = (path[0],)