### 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
if (SceneTree::get_singleton()->get_root()->is_embedding_subwindows() || !EDITOR_GET("interface/multi_window/enable")) {
		return;
	}
	window = memnew(Window);
	window->set_wrap_controls(true);
	add_child(window);
	window->hide();
	window->connect("close_requested", callable_mp(this, &WindowWrapper::set_window_enabled).bind(false));
	ShortcutBin *capturer = memnew(ShortcutBin);
	window->add_child(capturer);
	window_background = memnew(Panel);
	window_background->set_anchors_and_offsets_preset(PRESET_FULL_RECT);
	window->add_child(window_background);
}
void ScreenSelect::_build_advanced_menu() {