### 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)

DisplayServerWindows *ds_win = static_cast<DisplayServerWindows *>(DisplayServer::get_singleton());
	if (ds_win) {
		return ds_win->WndProc(hWnd, uMsg, wParam, lParam);
	} else {
		return DefWindowProcW(hWnd, uMsg, wParam, lParam);
	}
}
void DisplayServerWindows::_process_activate_event(WindowID p_window_id, WPARAM wParam, LPARAM lParam) {
	if (LOWORD(wParam) == WA_ACTIVE || LOWORD(wParam) == WA_CLICKACTIVE) {
		_send_window_event(windows[p_window_id], WINDOW_EVENT_FOCUS_IN);
		windows[p_window_id].window_focused = true;
		alt_mem = false;
		control_mem = false;
		shift_mem = false;
		gr_mem = false;
		
		_set_mouse_mode_impl(mouse_mode);
	} else { 
		Input::get_singleton()->release_pressed_events();
		_send_window_event(windows[p_window_id], WINDOW_EVENT_FOCUS_OUT);
		windows[p_window_id].window_focused = false;
		alt_mem = false;
	}
	if ((tablet_get_current_driver() == "wintab") && wintab_available && windows[p_window_id].wtctx) {
		wintab_WTEnable(windows[p_window_id].wtctx, GET_WM_ACTIVATE_STATE(wParam, lParam));
	}
}
void DisplayServerWindows::_process_key_events() {