### 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)

while (XCheckIfEvent(x11_display, &ev, _predicate_clipboard_save_targets, (XPointer)&x11_window)) {
			switch (ev.type) {
				case SelectionRequest:
					_handle_selection_request_event(&(ev.xselectionrequest));
					break;
				case SelectionNotify: {
					if (ev.xselection.target == save_targets) {
						
						return;
					}
					break;
				}
			}
		}
	}
}
int DisplayServerX11::get_screen_count() const {
	_THREAD_SAFE_METHOD_
	int count = 0;
	
	int event_base, error_base;
	if (XineramaQueryExtension(x11_display, &event_base, &error_base)) {
		XineramaScreenInfo *xsi = XineramaQueryScreens(x11_display, &count);
		XFree(xsi);
	} else {
		count = XScreenCount(x11_display);
	}
	return count;
}
int DisplayServerX11::get_primary_screen() const {