### Godot version

v4.2.dev.custom_build [0c2144da9]

### System information

Debian Linux X11 Xfce

### Issue description

Prerequisite: Be in Single Window Mode in the Editor
The Filesystem Dock is unusable when it is floating, which is not expected.
It appears garbled in the top-left corner:
![image](https://github.com/godotengine/godot/assets/6299227/109f7922-97de-44c3-814a-ca7f970e0602)

The following errors are shown:
```
  editor/window_wrapper.cpp:220 - Condition "!is_window_available()" is true.
  editor/window_wrapper.cpp:202 - Condition "!get_window_enabled()" is true. Returning: Rect2i()
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
```

bisecting lead to #62378
possibly related to #44439

### Steps to reproduce

1. Start a project in the Editor
2. Switch to Single Window Mode in the Editor and reload (if necessary)
3. Make the Filesystem Dock floating

### Minimal reproduction project

Editor issue
emit_signal("request_open_in_screen", p_screen_idx);
}
void ScreenSelect::_bind_methods() {
	ADD_SIGNAL(MethodInfo("request_open_in_screen", PropertyInfo(Variant::INT, "screen")));
}
void ScreenSelect::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_READY: {
			connect("gui_input", callable_mp(this, &ScreenSelect::_handle_mouse_shortcut));
		} break;
		case NOTIFICATION_THEME_CHANGED: {
			set_icon(EditorNode::get_singleton()->get_gui_base()->get_theme_icon("MakeFloating", "EditorIcons"));
			popup_background->add_theme_style_override("panel", get_theme_stylebox("PanelForeground", "EditorStyles"));
			const real_t popup_height = real_t(get_theme_font_size("font_size")) * 2.0;
			popup->set_min_size(Size2(0, popup_height * 3));
		} break;
	}
}
void ScreenSelect::_handle_mouse_shortcut(const Ref<InputEvent> &p_event) {
	const Ref<InputEventMouseButton> mouse_button = p_event;
	if (mouse_button.is_valid()) {
		if (mouse_button->is_pressed() && mouse_button->get_button_index() == MouseButton::LEFT) {
			_emit_screen_signal(get_window()->get_current_screen());
			accept_event();
		}
	}
}
void ScreenSelect::_show_popup() {