### 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)

String ret;
	Window selection_owner = XGetSelectionOwner(x11_display, p_source);
	if (selection_owner == x11_window) {
		static const char *target_type = "PRIMARY";
		if (p_source != None && get_atom_name(x11_display, p_source) == target_type) {
			return internal_clipboard_primary;
		} else {
			return internal_clipboard;
		}
	}
	if (selection_owner != None) {
		
		MutexLock mutex_lock(events_mutex);
		Atom selection = XA_PRIMARY;
		XConvertSelection(x11_display, p_source, target, selection,
				x11_window, CurrentTime);
		XFlush(x11_display);
		
		XEvent event;
		XIfEvent(x11_display, &event, _predicate_clipboard_selection, (XPointer)&x11_window);
		
		Atom type;
		int format, result;
		unsigned long len, bytes_left, dummy;
		unsigned char *data;
		XGetWindowProperty(x11_display, x11_window,
				selection,