### 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
gui_base->add_child(video_restart_dialog);
	progress_hb = memnew(BackgroundProgress);
	layout_dialog = memnew(EditorLayoutsDialog);
	gui_base->add_child(layout_dialog);
	layout_dialog->set_hide_on_ok(false);
	layout_dialog->set_size(Size2(225, 270) * EDSCALE);
	layout_dialog->connect("name_confirmed", callable_mp(this, &EditorNode::_dialog_action));
	update_spinner = memnew(MenuButton);
	right_menu_hb->add_child(update_spinner);
	update_spinner->set_icon(gui_base->get_theme_icon(SNAME("Progress1"), SNAME("EditorIcons")));
	update_spinner->get_popup()->connect("id_pressed", callable_mp(this, &EditorNode::_menu_option));
	PopupMenu *p = update_spinner->get_popup();
	p->add_radio_check_item(TTR("Update Continuously"), SETTINGS_UPDATE_CONTINUOUSLY);
	p->add_radio_check_item(TTR("Update When Changed"), SETTINGS_UPDATE_WHEN_CHANGED);
	p->add_separator();
	p->add_item(TTR("Hide Update Spinner"), SETTINGS_UPDATE_SPINNER_HIDE);
	_update_update_spinner();
	
	memnew(SceneTreeDock(scene_root, editor_selection, editor_data));
	memnew(InspectorDock(editor_data));
	memnew(ImportDock);
	memnew(NodeDock);
	FileSystemDock *filesystem_dock = memnew(FileSystemDock);
	filesystem_dock->connect("inherit", callable_mp(this, &EditorNode::_inherit_request));
	filesystem_dock->connect("instantiate", callable_mp(this, &EditorNode::_instantiate_request));
	filesystem_dock->connect("display_mode_changed", callable_mp(this, &EditorNode::_save_editor_layout));
	get_project_settings()->connect_filesystem_dock_signals(filesystem_dock);
	history_dock = memnew(HistoryDock);
	
	dock_slot[DOCK_SLOT_LEFT_UR]->add_child(SceneTreeDock::get_singleton());