### 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)

_send_window_event(windows[C->get()], DisplayServerWindows::WINDOW_EVENT_CLOSE_REQUEST);
		}
		time_since_popup = OS::get_singleton()->get_ticks_msec();
		popup_list.push_back(p_window);
	}
}
void DisplayServerWindows::popup_close(WindowID p_window) {
	_THREAD_SAFE_METHOD_
	List<WindowID>::Element *E = popup_list.find(p_window);
	while (E) {
		List<WindowID>::Element *F = E->next();
		WindowID win_id = E->get();
		popup_list.erase(E);
		if (win_id != p_window) {
			
			_send_window_event(windows[win_id], DisplayServerWindows::WINDOW_EVENT_CLOSE_REQUEST);
		}
		E = F;
	}
}
LRESULT DisplayServerWindows::MouseProc(int code, WPARAM wParam, LPARAM lParam) {
	_THREAD_SAFE_METHOD_
	uint64_t delta = OS::get_singleton()->get_ticks_msec() - time_since_popup;
	if (delta > 250) {
		switch (wParam) {
			case WM_NCLBUTTONDOWN:
			case WM_NCRBUTTONDOWN:
			case WM_NCMBUTTONDOWN:
			case WM_LBUTTONDOWN:
			case WM_RBUTTONDOWN: