### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

case WM_MBUTTONDOWN: {
				MOUSEHOOKSTRUCT *ms = (MOUSEHOOKSTRUCT *)lParam;
				Point2i pos = Point2i(ms->pt.x, ms->pt.y) - _get_screens_origin();
				List<WindowID>::Element *C = nullptr;
				List<WindowID>::Element *E = popup_list.back();
				
				while (E) {
					
					Rect2i win_rect = Rect2i(window_get_position(E->get()), window_get_size(E->get()));
					
					Rect2i safe_rect = window_get_popup_safe_rect(E->get());
					if (win_rect.has_point(pos)) {
						break;
					} else if (safe_rect != Rect2i() && safe_rect.has_point(pos)) {
						break;
					} else {
						C = E;
						E = E->prev();
					}
				}
				if (C) {
					_send_window_event(windows[C->get()], DisplayServerWindows::WINDOW_EVENT_CLOSE_REQUEST);
					return 1;
				}
			} break;
		}
	}
	return ::CallNextHookEx(mouse_monitor, code, wParam, lParam);
}
LRESULT DisplayServerWindows::_handle_early_window_message(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {