### 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)

Key modifiers = p_keycode & KeyModifierMask::MODIFIER_MASK;
	Key keycode_no_mod = p_keycode & KeyModifierMask::CODE_MASK;
	unsigned int xkeycode = KeyMappingX11::get_xlibcode(keycode_no_mod);
	KeySym xkeysym = XkbKeycodeToKeysym(x11_display, xkeycode, keyboard_get_current_layout(), 0);
	if (is_ascii_lower_case(xkeysym)) {
		xkeysym -= ('a' - 'A');
	}
	Key key = KeyMappingX11::get_keycode(xkeysym);
	
	
	if (key == Key::NONE) {
		return p_keycode;
	}
	return (Key)(key | modifiers);
}
DisplayServerX11::Property DisplayServerX11::_read_property(Display *p_display, Window p_window, Atom p_property) {