### 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)

SetCursorPos(pos.x, pos.y);
			}
			mm->set_velocity(Input::get_singleton()->get_last_mouse_velocity());
			if (old_invalid) {
				old_x = mm->get_position().x;
				old_y = mm->get_position().y;
				old_invalid = false;
			}
			mm->set_relative(Vector2(mm->get_position() - Vector2(old_x, old_y)));
			old_x = mm->get_position().x;
			old_y = mm->get_position().y;
			if (receiving_window_id != window_id) {
				
				mm->set_position(mm->get_position() - window_get_position(receiving_window_id) + window_get_position(window_id));
				mm->set_global_position(mm->get_position());
			}
			Input::get_singleton()->parse_input_event(mm);
		} break;
		case WM_LBUTTONDOWN:
		case WM_LBUTTONUP:
			if (Input::get_singleton()->is_emulating_mouse_from_touch()) {
				
				LPARAM extra = GetMessageExtraInfo();
				if (IsTouchEvent(extra)) {
					break;
				}
			}
			[[fallthrough]];
		case WM_MBUTTONDOWN:
		case WM_MBUTTONUP: