### 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
case FILE_EXPORT_PROJECT: {
			project_export->popup_export();
		} break;
		case FILE_EXTERNAL_OPEN_SCENE: {
			if (unsaved_cache && !p_confirmed) {
				confirmation->set_ok_button_text(TTR("Open"));
				confirmation->set_text(TTR("Current scene not saved. Open anyway?"));
				confirmation->popup_centered();
				break;
			}
			bool oprev = opening_prev;
			Error err = load_scene(external_file);
			if (err == OK && oprev) {
				previous_scenes.pop_back();
				opening_prev = false;
			}
		} break;
		case EDIT_UNDO: {
			if ((int)Input::get_singleton()->get_mouse_button_mask() & 0x7) {
				log->add_message(TTR("Can't undo while mouse buttons are pressed."), EditorLog::MSG_TYPE_EDITOR);
			} else {
				EditorUndoRedoManager *undo_redo = EditorUndoRedoManager::get_singleton();
				String action = undo_redo->get_current_action_name();
				int id = undo_redo->get_current_action_history_id();
				if (!undo_redo->undo()) {
					log->add_message(TTR("Nothing to undo."), EditorLog::MSG_TYPE_EDITOR);
				} else if (!action.is_empty()) {
					switch (id) {
						case EditorUndoRedoManager::GLOBAL_HISTORY:
							log->add_message(vformat(TTR("Global Undo: %s"), action), EditorLog::MSG_TYPE_EDITOR);