### 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)

_THREAD_SAFE_METHOD_
	p_screen = _get_screen_index(p_screen);
	ERR_FAIL_INDEX_V(p_screen, get_screen_count(), 0);
	
	Size2i sc = screen_get_size(p_screen);
	if (xrandr_ext_ok) {
		int count = 0;
		if (xrr_get_monitors) {
			xrr_monitor_info *monitors = xrr_get_monitors(x11_display, windows[MAIN_WINDOW_ID].x11_window, true, &count);
			if (p_screen < count) {
				double xdpi = sc.width / (double)monitors[p_screen].mwidth * 25.4;
				double ydpi = sc.height / (double)monitors[p_screen].mheight * 25.4;
				xrr_free_monitors(monitors);
				return (xdpi + ydpi) / 2;
			}
			xrr_free_monitors(monitors);
		} else if (p_screen == 0) {
			XRRScreenSize *sizes = XRRSizes(x11_display, 0, &count);
			if (sizes) {
				double xdpi = sc.width / (double)sizes[0].mwidth * 25.4;
				double ydpi = sc.height / (double)sizes[0].mheight * 25.4;
				return (xdpi + ydpi) / 2;
			}
		}
	}
	int width_mm = DisplayWidthMM(x11_display, p_screen);