### 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
Node *scene = editor_data.get_edited_scene_root(idx);
	if (!scene) {
		show_accept(TTR("This operation can't be done without a tree root."), TTR("OK"));
		return;
	}
	if (!scene->get_scene_file_path().is_empty() && _validate_scene_recursive(scene->get_scene_file_path(), scene)) {
		show_accept(TTR("This scene can't be saved because there is a cyclic instance inclusion.\nPlease resolve it and then attempt to save again."), TTR("OK"));
		return;
	}
	scene->propagate_notification(NOTIFICATION_EDITOR_PRE_SAVE);
	editor_data.apply_changes_in_editors();
	List<Ref<AnimatedValuesBackup>> anim_backups;
	_reset_animation_players(scene, &anim_backups);
	save_default_environment();
	_save_editor_states(p_file, idx);
	Ref<PackedScene> sdata;
	if (ResourceCache::has(p_file)) {
		
		
		
		sdata = ResourceCache::get_ref(p_file);
		if (sdata.is_valid()) {
			sdata->recreate_state();
		} else {
			sdata.instantiate();
		}
	} else {
		sdata.instantiate();
	}
	Error err = sdata->pack(scene);