### 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
if (!root_node_selected) {
				desc += "\n" + TTR("Hold Shift when dropping to add as sibling of selected node.");
			}
			if (texture != nullptr) {
				Sprite2D *sprite = memnew(Sprite2D);
				sprite->set_texture(texture);
				sprite->set_modulate(Color(1, 1, 1, 0.7f));
				preview_node->add_child(sprite);
				label->show();
				label_desc->show();
				desc += "\n" + TTR("Hold Alt when dropping to add as a different node type.");
				label_desc->set_text(desc);
			} else {
				if (scene.is_valid()) {
					Node *instance = scene->instantiate();
					if (instance) {
						preview_node->add_child(instance);
						label_desc->show();
						label_desc->set_text(desc);
					}
				}
			}
			add_preview = true;
		}
	}
	if (add_preview) {
		EditorNode::get_singleton()->get_scene_root()->add_child(preview_node);
	}
}
void CanvasItemEditorViewport::_remove_preview() {