Block adding an object to itself (by using .add) as it causes infinite recursive loop on PanObject.vsys()

[AnthoBalitrand]

Describe the bug

It is actually possible to add an object to itself (using the PanObject.add() method), which can causes infinite depth recursivity issue when using delete() or delete_similar() on it.

Possible solution

Avoid the possibility of adding an object to itself through the PanObject.add() method.