### 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_
	ERR_FAIL_COND(!windows.has(p_window));
	windows[p_window].mpath = p_region;
	_update_window_mouse_passthrough(p_window);
}
void DisplayServerWindows::_update_window_mouse_passthrough(WindowID p_window) {
	ERR_FAIL_COND(!windows.has(p_window));
	if (windows[p_window].mpass || windows[p_window].mpath.size() == 0) {
		SetWindowRgn(windows[p_window].hWnd, nullptr, TRUE);
	} else {
		POINT *points = (POINT *)memalloc(sizeof(POINT) * windows[p_window].mpath.size());
		for (int i = 0; i < windows[p_window].mpath.size(); i++) {
			if (windows[p_window].borderless) {
				points[i].x = windows[p_window].mpath[i].x;
				points[i].y = windows[p_window].mpath[i].y;
			} else {
				points[i].x = windows[p_window].mpath[i].x + GetSystemMetrics(SM_CXSIZEFRAME);
				points[i].y = windows[p_window].mpath[i].y + GetSystemMetrics(SM_CYSIZEFRAME) + GetSystemMetrics(SM_CYCAPTION);
			}
		}
		HRGN region = CreatePolygonRgn(points, windows[p_window].mpath.size(), ALTERNATE);
		SetWindowRgn(windows[p_window].hWnd, region, TRUE);
		DeleteObject(region);
		memfree(points);
	}
}
int DisplayServerWindows::window_get_current_screen(WindowID p_window) const {