### 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
update_spinner->set_visible(EDITOR_GET("interface/editor/show_update_spinner"));
	const bool update_continuously = EDITOR_GET("interface/editor/update_continuously");
	PopupMenu *update_popup = update_spinner->get_popup();
	update_popup->set_item_checked(update_popup->get_item_index(SETTINGS_UPDATE_CONTINUOUSLY), update_continuously);
	update_popup->set_item_checked(update_popup->get_item_index(SETTINGS_UPDATE_WHEN_CHANGED), !update_continuously);
	if (update_continuously) {
		update_spinner->set_tooltip_text(TTR("Spins when the editor window redraws.\nUpdate Continuously is enabled, which can increase power usage. Click to disable it."));
		
		
		
		
		const bool dark_theme = EditorSettings::get_singleton()->is_dark_theme();
		update_spinner->set_self_modulate(
				gui_base->get_theme_color(SNAME("error_color"), SNAME("Editor")) * (dark_theme ? Color(1.1, 1.1, 1.1) : Color(4.25, 4.25, 4.25)));
	} else {
		update_spinner->set_tooltip_text(TTR("Spins when the editor window redraws."));
		update_spinner->set_self_modulate(Color(1, 1, 1));
	}
	OS::get_singleton()->set_low_processor_usage_mode(!update_continuously);
}
void EditorNode::_on_plugin_ready(Object *p_script, const String &p_activate_name) {