### 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
}
			img->convert(Image::FORMAT_RGB8);
			
			String temp_path = EditorPaths::get_singleton()->get_cache_dir();
			String cache_base = ProjectSettings::get_singleton()->globalize_path(p_file).md5_text();
			cache_base = temp_path.path_join("resthumb-" + cache_base);
			
			post_process_preview(img);
			img->save_png(cache_base + ".png");
		}
	}
	save.step(TTR("Saving Scene"), 4);
	_save_scene(p_file, p_idx);
	if (!singleton->cmdline_export_mode) {
		EditorResourcePreview::get_singleton()->check_for_invalidation(p_file);
	}
}
bool EditorNode::_validate_scene_recursive(const String &p_filename, Node *p_node) {
	for (int i = 0; i < p_node->get_child_count(); i++) {
		Node *child = p_node->get_child(i);
		if (child->get_scene_file_path() == p_filename) {
			return true;
		}
		if (_validate_scene_recursive(p_filename, child)) {
			return true;
		}
	}
	return false;
}
int EditorNode::_save_external_resources() {