gui: fix bug when adding new receiver to tray menu

lib/solaar/ui/tray.py

@@ -409,7 +409,7 @@ def _add_receiver(receiver):
 
     new_receiver_info = (receiver.path, None, receiver.name, None)
     assert len(new_receiver_info) == len(_RECEIVER_SEPARATOR)
-    _devices_info.append(new_receiver_info)
+    _devices_info.insert(0, new_receiver_info)
 
     new_menu_item = Gtk.ImageMenuItem.new_with_label(receiver.name)
     icon_set = _icons.device_icon_set(receiver.name)

lib/solaar/ui/window.py

@@ -879,7 +879,8 @@ def update(device, need_popup=False, refresh=False):
         elif item:
             if _TREE_SEPATATOR:
                 separator = _model.iter_next(item)
-                _model.remove(separator)
+                if separator:
+                    _model.remove(separator)
             _model.remove(item)
 
     else: