### 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)

Atom workarea_prop = XInternAtom(x11_display, "_NET_WORKAREA", True);
		if (workarea_prop != None) {
			unsigned long workarea_len = 0;
			unsigned char *workarea_data = nullptr;
			if (XGetWindowProperty(x11_display, x11_window, workarea_prop, 0, LONG_MAX, False, XA_CARDINAL, &type, &format, &workarea_len, &remaining, &workarea_data) == Success) {
				if ((format == 32) && (workarea_len >= ((desktop_index + 1) * 4)) && workarea_data) {
					long *rect_data = (long *)workarea_data;
					int data_offset = desktop_index * 4;
					Rect2i workarea_rect;
					workarea_rect.position.x = rect_data[data_offset];
					workarea_rect.position.y = rect_data[data_offset + 1];
					workarea_rect.size.x = rect_data[data_offset + 2];
					workarea_rect.size.y = rect_data[data_offset + 3];
					
					if (!is_multiscreen) {
						rect = workarea_rect;
					} else if (rect.intersects(workarea_rect)) {
						rect = rect.intersection(workarea_rect);
					}
				}
			}
			if (workarea_data) {
				XFree(workarea_data);
			}
		}
	}
	return rect;
}
int DisplayServerX11::screen_get_dpi(int p_screen) const {