### 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
HBoxContainer *top_menu = memnew(HBoxContainer);
	add_child(top_menu);
	theme_name = memnew(Label);
	theme_name->set_text(TTR("Theme:"));
	theme_name->set_theme_type_variation("HeaderSmall");
	top_menu->add_child(theme_name);
	top_menu->add_spacer(false);
	Button *theme_save_button = memnew(Button);
	theme_save_button->set_text(TTR("Save"));
	theme_save_button->set_flat(true);
	theme_save_button->connect("pressed", callable_mp(this, &ThemeEditor::_theme_save_button_cbk).bind(false));
	top_menu->add_child(theme_save_button);
	Button *theme_save_as_button = memnew(Button);
	theme_save_as_button->set_text(TTR("Save As..."));
	theme_save_as_button->set_flat(true);
	theme_save_as_button->connect("pressed", callable_mp(this, &ThemeEditor::_theme_save_button_cbk).bind(true));
	top_menu->add_child(theme_save_as_button);
	top_menu->add_child(memnew(VSeparator));
	Button *theme_edit_button = memnew(Button);
	theme_edit_button->set_text(TTR("Manage Items..."));