### 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
_update_update_spinner();
		} break;
		case SETTINGS_PREFERENCES: {
			editor_settings_dialog->popup_edit_settings();
		} break;
		case SETTINGS_EDITOR_DATA_FOLDER: {
			OS::get_singleton()->shell_show_in_file_manager(EditorPaths::get_singleton()->get_data_dir(), true);
		} break;
		case SETTINGS_EDITOR_CONFIG_FOLDER: {
			OS::get_singleton()->shell_show_in_file_manager(EditorPaths::get_singleton()->get_config_dir(), true);
		} break;
		case SETTINGS_MANAGE_EXPORT_TEMPLATES: {
			export_template_manager->popup_manager();
		} break;
		case SETTINGS_MANAGE_FBX_IMPORTER: {
#if !defined(ANDROID_ENABLED) && !defined(WEB_ENABLED)
			fbx_importer_manager->show_dialog();
#endif
		} break;
		case SETTINGS_INSTALL_ANDROID_BUILD_TEMPLATE: {
			gradle_build_manage_templates->hide();
			file_android_build_source->popup_centered_ratio();
		} break;
		case SETTINGS_MANAGE_FEATURE_PROFILES: {
			feature_profile_manager->popup_centered_clamped(Size2(900, 800) * EDSCALE, 0.8);
		} break;
		case SETTINGS_TOGGLE_FULLSCREEN: {
			DisplayServer::get_singleton()->window_set_mode(DisplayServer::get_singleton()->window_get_mode() == DisplayServer::WINDOW_MODE_FULLSCREEN ? DisplayServer::WINDOW_MODE_WINDOWED : DisplayServer::WINDOW_MODE_FULLSCREEN);
		} break;
		case EDITOR_SCREENSHOT: {