### 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
saving_resource = Ref<Resource>();
			ObjectID current_id = editor_history.get_current();
			Object *current_obj = current_id.is_valid() ? ObjectDB::get_instance(current_id) : nullptr;
			ERR_FAIL_COND(!current_obj);
			current_obj->notify_property_list_changed();
		} break;
		case SETTINGS_LAYOUT_SAVE: {
			if (p_file.is_empty()) {
				return;
			}
			Ref<ConfigFile> config;
			config.instantiate();
			Error err = config->load(EditorSettings::get_singleton()->get_editor_layouts_config());
			if (err == ERR_FILE_CANT_OPEN || err == ERR_FILE_NOT_FOUND) {
				config.instantiate();
			} else if (err != OK) {
				show_warning(TTR("An error occurred while trying to save the editor layout.\nMake sure the editor's user data path is writable."));
				return;
			}
			_save_docks_to_config(config, p_file);
			config->save(EditorSettings::get_singleton()->get_editor_layouts_config());
			layout_dialog->hide();
			_update_layouts_menu();
			if (p_file == "Default") {
				show_warning(TTR("Default editor layout overridden.\nTo restore the Default layout to its base settings, use the Delete Layout option and delete the Default layout."));
			}
		} break;
		case SETTINGS_LAYOUT_DELETE: {
			if (p_file.is_empty()) {
				return;