### 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 Vector2i();
	}
	int cursor = ImmGetCompositionStringW(wd.im_himc, GCS_CURSORPOS, nullptr, 0);
	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);
	int32_t utf32_cursor = 0;
	for (int32_t i = 0; i < length / int32_t(sizeof(wchar_t)); i++) {
		if ((string[i] & 0xfffffc00) == 0xd800) {
			i++;
		}
		if (i < cursor) {
			utf32_cursor++;
		} else {
			break;
		}
	}
	memdelete(string);
	return Vector2i(utf32_cursor, 0);
}
String DisplayServerWindows::ime_get_text() const {