### 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 (abs_info) {
							
							Vector2 mult = abs_info->value;
							xi.relative_motion.x += (xi.raw_pos.x - xi.old_raw_pos.x) * mult.x;
							xi.relative_motion.y += (xi.raw_pos.y - xi.old_raw_pos.y) * mult.y;
						} else {
							
							xi.relative_motion.x = xi.raw_pos.x;
							xi.relative_motion.y = xi.raw_pos.y;
						}
						xi.last_relative_time = raw_event->time;
					} break;
#ifdef TOUCH_ENABLED
					case XI_TouchBegin:
					case XI_TouchEnd: {
						if (ime_window_event || ignore_events) {
							break;
						}
						bool is_begin = event_data->evtype == XI_TouchBegin;
						Ref<InputEventScreenTouch> st;
						st.instantiate();
						st->set_window_id(window_id);
						st->set_index(index);
						st->set_position(pos);
						st->set_pressed(is_begin);
						if (is_begin) {
							if (xi.state.has(index)) { 
								break;
							}
							xi.state[index] = pos;