### 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_
	DisplayServer::WindowID window_id = _get_focused_window_or_popup();
	const WindowData &wd = windows[window_id];
	if (!wd.ime_active) {
		return String();
	}
	String ret;
	int32_t length = ImmGetCompositionStringW(wd.im_himc, GCS_COMPSTR, nullptr, 0);
	wchar_t *string = reinterpret_cast<wchar_t *>(memalloc(length));
	ImmGetCompositionStringW(wd.im_himc, GCS_COMPSTR, string, length);
	ret.parse_utf16((char16_t *)string, length / sizeof(wchar_t));
	memdelete(string);
	return ret;
}
void DisplayServerWindows::window_set_ime_active(const bool p_active, WindowID p_window) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	if (p_active) {
		wd.ime_active = true;
		ImmAssociateContext(wd.hWnd, wd.im_himc);
		CreateCaret(wd.hWnd, NULL, 1, 1);
		window_set_ime_position(wd.im_position, p_window);
	} else {
		ImmAssociateContext(wd.hWnd, (HIMC)0);
		DestroyCaret();
		wd.ime_active = false;
	}
}
void DisplayServerWindows::window_set_ime_position(const Point2i &p_pos, WindowID p_window) {