### 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)

#ifdef GLES3_ENABLED
		if (gl_manager) {
			Error err = gl_manager->window_create(id, wd.x11_window, x11_display, win_rect.size.width, win_rect.size.height);
			ERR_FAIL_COND_V_MSG(err != OK, INVALID_WINDOW_ID, "Can't create an OpenGL window");
			window_set_vsync_mode(p_vsync_mode, id);
		}
#endif
		
		XFlush(x11_display);
		XSync(x11_display, False);
		
	}
	window_set_mode(p_mode, id);
	
	{
		XWindowAttributes xwa;
		XSync(x11_display, False);
		XGetWindowAttributes(x11_display, wd.x11_window, &xwa);
		wd.position.x = xwa.x;
		wd.position.y = xwa.y;
		wd.size.width = xwa.width;
		wd.size.height = xwa.height;
	}
	
	if (cursors[current_cursor] != None) {
		XDefineCursor(x11_display, wd.x11_window, cursors[current_cursor]);
	}
	return id;
}
static bool _is_xim_style_supported(const ::XIMStyle &p_style) {