### 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)

if (direct_touch) {
			xi.touch_devices.push_back(dev->deviceid);
			print_verbose("XInput: Using touch device: " + String(dev->name));
		}
		if (absolute_mode) {
			
			if (resolution_x <= 0) {
				resolution_x = (abs_x_max - abs_x_min) * abs_resolution_range_mult;
			}
			if (resolution_y <= 0) {
				resolution_y = (abs_y_max - abs_y_min) * abs_resolution_range_mult;
			}
			xi.absolute_devices[dev->deviceid] = Vector2(abs_resolution_mult / resolution_x, abs_resolution_mult / resolution_y);
			print_verbose("XInput: Absolute pointing device: " + String(dev->name));
		}
		xi.pressure = 0;
		xi.pen_pressure_range[dev->deviceid] = Vector2(pressure_min, pressure_max);
		xi.pen_tilt_x_range[dev->deviceid] = Vector2(tilt_x_min, tilt_x_max);
		xi.pen_tilt_y_range[dev->deviceid] = Vector2(tilt_y_min, tilt_y_max);
		xi.pen_inverted_devices[dev->deviceid] = String(dev->name).findn("eraser") > 0;
	}
	XIFreeDeviceInfo(info);
#ifdef TOUCH_ENABLED
	if (!xi.touch_devices.size()) {
		print_verbose("XInput: No touch devices found.");
	}
#endif
	return true;
}
void DisplayServerX11::_flush_mouse_motion() {