### 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)

return im_selection;
}
String DisplayServerX11::ime_get_text() const {
	return im_text;
}
void DisplayServerX11::cursor_set_shape(CursorShape p_shape) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_INDEX(p_shape, CURSOR_MAX);
	if (p_shape == current_cursor) {
		return;
	}
	if (mouse_mode == MOUSE_MODE_VISIBLE || mouse_mode == MOUSE_MODE_CONFINED) {
		if (cursors[p_shape] != None) {
			for (const KeyValue<WindowID, WindowData> &E : windows) {
				XDefineCursor(x11_display, E.value.x11_window, cursors[p_shape]);
			}
		} else if (cursors[CURSOR_ARROW] != None) {
			for (const KeyValue<WindowID, WindowData> &E : windows) {
				XDefineCursor(x11_display, E.value.x11_window, cursors[CURSOR_ARROW]);
			}
		}
	}
	current_cursor = p_shape;
}
DisplayServerX11::CursorShape DisplayServerX11::cursor_get_shape() const {