### 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)

::Time threshold = ABSDIFF(peek_event.xkey.time, xkeyevent->time);
#undef ABSDIFF
			if (peek_event.type == KeyPress && threshold < 5) {
				KeySym rk;
				XLookupString((XKeyEvent *)&peek_event, str, 256, &rk, nullptr);
				if (rk == keysym_keycode) {
					
					++p_event_index;
					_handle_key_event(p_window, (XKeyEvent *)&peek_event, p_events, p_event_index, true);
					return; 
				}
			}
			
		}
		
	}
	
	k->set_pressed(keypress);
	if (keycode >= Key::A + 32 && keycode <= Key::Z + 32) {
		keycode -= int('a' - 'A');
	}
	k->set_keycode(keycode);
	k->set_physical_keycode((Key)physical_keycode);
	if (!keysym.is_empty()) {
		k->set_key_label(fix_key_label(keysym[0], keycode));
	} else {
		k->set_key_label(keycode);
	}
	if (keypress) {
		k->set_unicode(fix_unicode(unicode));