### 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
edit_items_add_stylebox->set_disabled(true);
		edit_items_remove_class->set_disabled(true);
		edit_items_remove_custom->set_disabled(true);
		edit_items_remove_all->set_disabled(true);
		edit_items_message->set_text(TTR("Select a theme type from the list to edit its items.\nYou can add a custom type or import a type with its items from another theme."));
		edit_items_message->show();
	}
	_update_edit_item_tree(selected_type);
}
void ThemeItemEditorDialog::_edited_type_selected() {
	TreeItem *selected_item = edit_type_list->get_selected();
	String selected_type = selected_item->get_text(0);
	_update_edit_item_tree(selected_type);
}
void ThemeItemEditorDialog::_edited_type_button_pressed(Object *p_item, int p_column, int p_id, MouseButton p_button) {
	if (p_button != MouseButton::LEFT) {
		return;
	}
	TreeItem *item = Object::cast_to<TreeItem>(p_item);
	if (!item) {
		return;
	}
	switch (p_id) {
		case TYPES_TREE_REMOVE_ITEM: {
			String type_name = item->get_text(0);
			_remove_theme_type(type_name);
		} break;
	}
}
void ThemeItemEditorDialog::_update_edit_item_tree(String p_item_type) {