### 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
List<String> extensions;
			Ref<PackedScene> sd = memnew(PackedScene);
			ResourceSaver::get_recognized_extensions(sd, &extensions);
			file->clear_filters();
			for (int i = 0; i < extensions.size(); i++) {
				file->add_filter("*." + extensions[i], extensions[i].to_upper());
			}
			if (!scene->get_scene_file_path().is_empty()) {
				String path = scene->get_scene_file_path();
				file->set_current_path(path);
				if (extensions.size()) {
					String ext = path.get_extension().to_lower();
					if (extensions.find(ext) == nullptr) {
						file->set_current_path(path.replacen("." + ext, "." + extensions.front()->get()));
					}
				}
			} else if (extensions.size()) {
				String root_name = scene->get_name();
				root_name = EditorNode::adjust_scene_name_casing(root_name);
				file->set_current_path(root_name + "." + extensions.front()->get().to_lower());
			}
			file->popup_file_dialog();
			file->set_title(TTR("Save Scene As..."));
		} break;
		case FILE_SAVE_ALL_SCENES: {
			_save_all_scenes();
		} break;
		case FILE_RUN_SCENE: {
			project_run_bar->play_current_scene();
		} break;