### Godot version

41e5f5b0930343ef548a56d553ba20fafd672147

### System information

Windows 10, Vulkan, Intel® Core™ i7-8700K, Nvidia GTX 1080 (471.11)

### Issue description

The editor will crash if you select an AnimationTree node then select another node. This seems to be caused by the edit function assigning a null object via the edit interface, then calling another function which does not appear to be null.

### Steps to reproduce

Create an AnimationTree node then select another node.

### Minimal reproduction project

N/A
if (updating) {
		return;
	}
	_name_edited(name_edit->get_text());
}
void AnimationNodeStateMachineEditor::_scroll_changed(double) {
	if (updating) {
		return;
	}
	state_machine->set_graph_offset(Vector2(h_scroll->get_value(), v_scroll->get_value()));
	state_machine_draw->queue_redraw();
}
void AnimationNodeStateMachineEditor::_erase_selected(const bool p_nested_action) {