### 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)

int number_of_screens = XScreenCount(x11_display);
	for (int i = 0; i < number_of_screens; i++) {
		Window root, child;
		int root_x, root_y, win_x, win_y;
		unsigned int mask;
		if (XQueryPointer(x11_display, XRootWindow(x11_display, i), &root, &child, &root_x, &root_y, &win_x, &win_y, &mask)) {
			XWindowAttributes root_attrs;
			XGetWindowAttributes(x11_display, root, &root_attrs);
			return Vector2i(root_attrs.x + root_x, root_attrs.y + root_y);
		}
	}
	return Vector2i();
}
BitField<MouseButtonMask> DisplayServerX11::mouse_get_button_state() const {
	return last_button_state;
}
void DisplayServerX11::clipboard_set(const String &p_text) {
	_THREAD_SAFE_METHOD_
	{
		
		MutexLock mutex_lock(events_mutex);
		internal_clipboard = p_text;
	}
	XSetSelectionOwner(x11_display, XA_PRIMARY, windows[MAIN_WINDOW_ID].x11_window, CurrentTime);
	XSetSelectionOwner(x11_display, XInternAtom(x11_display, "CLIPBOARD", 0), windows[MAIN_WINDOW_ID].x11_window, CurrentTime);
}
void DisplayServerX11::clipboard_set_primary(const String &p_text) {