### 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
ERR_FAIL_COND(!is_window_available());
	ERR_FAIL_INDEX(p_screen, DisplayServer::get_singleton()->get_screen_count());
	_set_window_enabled_with_rect(true, p_rect);
	window->set_current_screen(p_screen);
}
void WindowWrapper::restore_window_from_saved_position(const Rect2 p_window_rect, int p_screen, const Rect2 p_screen_rect) {
	ERR_FAIL_COND(!is_window_available());
	Rect2 window_rect = p_window_rect;
	int screen = p_screen;
	Rect2 restored_screen_rect = p_screen_rect;
	if (screen < 0 || screen >= DisplayServer::get_singleton()->get_screen_count()) {
		
		screen = get_window()->get_window_id();
	}
	Rect2i real_screen_rect = DisplayServer::get_singleton()->screen_get_usable_rect(screen);
	if (restored_screen_rect == Rect2i()) {
		
		restored_screen_rect = real_screen_rect;
	}
	if (window_rect == Rect2i()) {
		
		window_rect = Rect2i(restored_screen_rect.position + restored_screen_rect.size / 4, restored_screen_rect.size / 2);
	}
	
	Vector2 screen_ratio = Vector2(real_screen_rect.size) / Vector2(restored_screen_rect.size);
	
	window_rect.position -= restored_screen_rect.position;
	window_rect = Rect2i(window_rect.position * screen_ratio, window_rect.size * screen_ratio);