### 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
main_menu->set_start_index(0); 
	main_menu->set_prefer_global_menu(global_menu);
	main_menu->set_switch_on_hover(true);
	file_menu = memnew(PopupMenu);
	file_menu->set_name(TTR("Scene"));
	main_menu->add_child(file_menu);
	main_menu->set_menu_tooltip(0, TTR("Operations with scene files."));
	prev_scene = memnew(Button);
	prev_scene->set_flat(true);
	prev_scene->set_icon(gui_base->get_theme_icon(SNAME("PrevScene"), SNAME("EditorIcons")));
	prev_scene->set_tooltip_text(TTR("Go to previously opened scene."));
	prev_scene->set_disabled(true);
	prev_scene->connect("pressed", callable_mp(this, &EditorNode::_menu_option).bind(FILE_OPEN_PREV));
	gui_base->add_child(prev_scene);
	prev_scene->set_position(Point2(3, 24));
	prev_scene->hide();
	accept = memnew(AcceptDialog);
	accept->set_unparent_when_invisible(true);
	save_accept = memnew(AcceptDialog);
	save_accept->set_unparent_when_invisible(true);
	save_accept->connect("confirmed", callable_mp(this, &EditorNode::_menu_option).bind((int)MenuOptions::FILE_SAVE_AS_SCENE));
	project_export = memnew(ProjectExportDialog);
	gui_base->add_child(project_export);
	dependency_error = memnew(DependencyErrorDialog);
	gui_base->add_child(dependency_error);
	dependency_fixer = memnew(DependencyEditor);
	gui_base->add_child(dependency_fixer);
	editor_settings_dialog = memnew(EditorSettingsDialog);
	gui_base->add_child(editor_settings_dialog);
	project_settings_editor = memnew(ProjectSettingsEditor(&editor_data));