### 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 (xi.state.size() == 1) {
								
								
								xi.mouse_pos_to_filter = pos;
							}
							Input::get_singleton()->parse_input_event(st);
						} else {
							if (!xi.state.has(index)) { 
								break;
							}
							xi.state.erase(index);
							Input::get_singleton()->parse_input_event(st);
						}
					} break;
					case XI_TouchUpdate: {
						if (ime_window_event || ignore_events) {
							break;
						}
						HashMap<int, Vector2>::Iterator curr_pos_elem = xi.state.find(index);
						if (!curr_pos_elem) { 
							break;
						}
						if (curr_pos_elem->value != pos) {
							Ref<InputEventScreenDrag> sd;
							sd.instantiate();
							sd->set_window_id(window_id);
							sd->set_index(index);
							sd->set_position(pos);
							sd->set_relative(pos - curr_pos_elem->value);
							Input::get_singleton()->parse_input_event(sd);