### 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
disambiguated_scene_names.append(editor_data.get_scene_title(i));
		full_path_names.append(editor_data.get_scene_path(i));
	}
	disambiguate_filenames(full_path_names, disambiguated_scene_names);
	
	scene_tabs->disconnect("tab_changed", callable_mp(this, &EditorNode::_scene_tab_changed));
	scene_tabs->clear_tabs();
	Ref<Texture2D> script_icon = gui_base->get_theme_icon(SNAME("Script"), SNAME("EditorIcons"));
	for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
		Node *type_node = editor_data.get_edited_scene_root(i);
		Ref<Texture2D> icon;
		if (type_node) {
			icon = EditorNode::get_singleton()->get_object_icon(type_node, "Node");
		}
		bool unsaved = EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_scene_history_id(i));
		scene_tabs->add_tab(disambiguated_scene_names[i] + (unsaved ? "(*)" : ""), icon);
		if (DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_GLOBAL_MENU)) {
			DisplayServer::get_singleton()->global_menu_add_item("_dock", editor_data.get_scene_title(i) + (unsaved ? "(*)" : ""), callable_mp(this, &EditorNode::_global_menu_scene), Callable(), i);
		}
		if (show_rb && editor_data.get_scene_root_script(i).is_valid()) {
			scene_tabs->set_tab_button_icon(i, script_icon);
		}
	}
	if (DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_GLOBAL_MENU)) {
		DisplayServer::get_singleton()->global_menu_add_separator("_dock");
		DisplayServer::get_singleton()->global_menu_add_item("_dock", TTR("New Window"), callable_mp(this, &EditorNode::_global_menu_new_window));
	}
	if (scene_tabs->get_tab_count() > 0) {
		scene_tabs->set_current_tab(editor_data.get_edited_scene());
	}