### Godot version

v4.0.beta.custom_build [eaf306e0b]

### System information

Windows 10

### Issue description

Selecting a `Window` node in the Editor's SceneTree results in the message
```
editor/editor_data.cpp:1058 - Parameter "p_node" is null.
```
and the Inspector shows empty content instead of the Window's properties.

I would expect, that clicking on a node in the SceneTree lets me edit the properties of the node.

Bisecting shows that this behavior got introduced in #71770

### Steps to reproduce

1. Create a Window node
2. Click on the Window node in the Editor's SceneTree

### Minimal reproduction project

N/A
_remove_preview();
	List<BaseButton *> btn_list;
	button_group->get_buttons(&btn_list);
	for (int i = 0; i < btn_list.size(); i++) {
		CheckBox *check = Object::cast_to<CheckBox>(btn_list[i]);
		check->set_pressed(check->get_text() == default_texture_node_type);
	}
	selector->set_title(vformat(TTR("Add %s"), default_texture_node_type));
	selector->popup_centered();
}
bool CanvasItemEditorViewport::_only_packed_scenes_selected() const {
	for (int i = 0; i < selected_files.size(); ++i) {
		if (ResourceLoader::load(selected_files[i])->get_class() != "PackedScene") {
			return false;
		}
	}
	return true;
}
void CanvasItemEditorViewport::drop_data(const Point2 &p_point, const Variant &p_data) {