### 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)

XGetWindowAttributes(x11_display, focus, &xwa);
		Rect2i window_rect = Rect2i(x, y, xwa.width, xwa.height);
		
		int screen_index = 0;
		int max_area = 0;
		for (int i = 0; i < count; i++) {
			Rect2i screen_rect = _screen_get_rect(i);
			Rect2i intersection = screen_rect.intersection(window_rect);
			int area = intersection.get_area();
			if (area > max_area) {
				max_area = area;
				screen_index = i;
			}
		}
		return screen_index;
	}
	return get_primary_screen();
}
Rect2i DisplayServerX11::_screen_get_rect(int p_screen) const {
	Rect2i rect(0, 0, 0, 0);
	p_screen = _get_screen_index(p_screen);
	ERR_FAIL_COND_V(p_screen < 0, rect);
	
	int event_base, error_base;
	if (XineramaQueryExtension(x11_display, &event_base, &error_base)) {
		int count;
		XineramaScreenInfo *xsi = XineramaQueryScreens(x11_display, &count);
		
		if (p_screen < count) {
			rect.position.x = xsi[p_screen].x_org;