### 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)

if (wd.no_focus) {
		windowAttributes.override_redirect = True;
		windowAttributes.save_under = True;
		valuemask |= CWOverrideRedirect | CWSaveUnder;
	}
	int rq_screen = get_screen_from_rect(p_rect);
	if (rq_screen < 0) {
		rq_screen = get_primary_screen(); 
	}
	Rect2i win_rect = p_rect;
	if (p_mode == WINDOW_MODE_FULLSCREEN || p_mode == WINDOW_MODE_EXCLUSIVE_FULLSCREEN) {
		Rect2i screen_rect = Rect2i(screen_get_position(rq_screen), screen_get_size(rq_screen));
		win_rect = screen_rect;
	} else {
		Rect2i srect = screen_get_usable_rect(rq_screen);
		Point2i wpos = p_rect.position;
		wpos.x = CLAMP(wpos.x, srect.position.x, srect.position.x + srect.size.width - p_rect.size.width / 3);
		wpos.y = CLAMP(wpos.y, srect.position.y, srect.position.y + srect.size.height - p_rect.size.height / 3);
		win_rect.position = wpos;
	}
	
	
	wd.position = win_rect.position;
	wd.size = win_rect.size;
	{
		wd.x11_window = XCreateWindow(x11_display, RootWindow(x11_display, visualInfo.screen), win_rect.position.x, win_rect.position.y, win_rect.size.width > 0 ? win_rect.size.width : 1, win_rect.size.height > 0 ? win_rect.size.height : 1, 0, visualInfo.depth, InputOutput, visualInfo.visual, valuemask, &windowAttributes);