### 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 (p_clear_errors) {
		load_errors->clear();
	}
	String lpath = ProjectSettings::get_singleton()->localize_path(p_scene);
	if (!lpath.begins_with("res:")) {
		show_accept(TTR("Error loading scene, it must be inside the project path. Use 'Import' to open the scene, then save it inside the project path."), TTR("OK"));
		opening_prev = false;
		return ERR_FILE_NOT_FOUND;
	}
	int prev = editor_data.get_edited_scene();
	int idx = editor_data.add_edited_scene(-1);
	if (!editor_data.get_edited_scene_root() && editor_data.get_edited_scene_count() == 2) {
		_remove_edited_scene();
	} else if (!p_silent_change_tab) {
		_scene_tab_changed(idx);
	} else {
		set_current_scene(idx);
	}
	dependency_errors.clear();
	Error err;
	Ref<PackedScene> sdata = ResourceLoader::load(lpath, "", ResourceFormatLoader::CACHE_MODE_REPLACE, &err);
	if (!sdata.is_valid()) {
		_dialog_display_load_error(lpath, err);
		opening_prev = false;
		if (prev != -1) {
			set_current_scene(prev);
			editor_data.remove_scene(idx);
		}
		return ERR_FILE_NOT_FOUND;