### 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)

_set_wm_maximized(p_window, true);
			}
			Atom wm_state = XInternAtom(x11_display, "_NET_WM_STATE", False);
			Atom wm_above = XInternAtom(x11_display, "_NET_WM_STATE_ABOVE", False);
			XClientMessageEvent xev;
			memset(&xev, 0, sizeof(xev));
			xev.type = ClientMessage;
			xev.window = wd.x11_window;
			xev.message_type = wm_state;
			xev.format = 32;
			xev.data.l[0] = p_enabled ? _NET_WM_STATE_ADD : _NET_WM_STATE_REMOVE;
			xev.data.l[1] = wm_above;
			xev.data.l[3] = 1;
			XSendEvent(x11_display, DefaultRootWindow(x11_display), False, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&xev);
			if (!p_enabled && !wd.fullscreen) {
				_set_wm_maximized(p_window, false);
			}
			wd.on_top = p_enabled;
		} break;
		case WINDOW_FLAG_TRANSPARENT: {
			wd.layered_window = p_enabled;
		} break;
		case WINDOW_FLAG_NO_FOCUS: {
			wd.no_focus = p_enabled;
		} break;
		case WINDOW_FLAG_MOUSE_PASSTHROUGH: {
			wd.mpass = p_enabled;
			_update_window_mouse_passthrough(p_window);
		} break;
		case WINDOW_FLAG_POPUP: {