### 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)

break;
							}
						}
					}
					if (window_id_other != INVALID_WINDOW_ID) {
						int x, y;
						Window child;
						XTranslateCoordinates(x11_display, wd.x11_window, wd_other_x11_window, event.xbutton.x, event.xbutton.y, &x, &y, &child);
						mb->set_window_id(window_id_other);
						mb->set_position(Vector2(x, y));
						mb->set_global_position(mb->get_position());
					}
				}
				Input::get_singleton()->parse_input_event(mb);
			} break;
			case MotionNotify: {
				if (ime_window_event || ignore_events) {
					break;
				}
				
				
				
				WindowID focused_window_id = _get_focused_window_or_popup();
				if (!windows.has(focused_window_id)) {
					focused_window_id = MAIN_WINDOW_ID;
				}
				while (true) {
					if (mouse_mode == MOUSE_MODE_CAPTURED && event.xmotion.x == windows[focused_window_id].size.width / 2 && event.xmotion.y == windows[focused_window_id].size.height / 2) {
						
						center = Vector2(event.xmotion.x, event.xmotion.y);