### 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)

xi.relative_motion.y = 0;
				if (mouse_mode == MOUSE_MODE_CAPTURED) {
					pos = Point2i(windows[focused_window_id].size.width / 2, windows[focused_window_id].size.height / 2);
				}
				Ref<InputEventMouseMotion> mm;
				mm.instantiate();
				mm->set_window_id(window_id);
				if (xi.pressure_supported) {
					mm->set_pressure(xi.pressure);
				} else {
					mm->set_pressure(bool(mouse_get_button_state().has_flag(MouseButtonMask::LEFT)) ? 1.0f : 0.0f);
				}
				mm->set_tilt(xi.tilt);
				mm->set_pen_inverted(xi.pen_inverted);
				_get_key_modifier_state(event.xmotion.state, mm);
				mm->set_button_mask(mouse_get_button_state());
				mm->set_position(pos);
				mm->set_global_position(pos);
				mm->set_velocity(Input::get_singleton()->get_last_mouse_velocity());
				mm->set_relative(rel);
				last_mouse_pos = pos;
				
				
				
				
				if (focused) {
					Input::get_singleton()->parse_input_event(mm);
				} else {