### 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)

k->set_physical_keycode(Key::TAB);
					k->set_shift_pressed(true);
				}
				Input::get_singleton()->parse_input_event(k);
			}
			memfree(utf8string);
			return;
		}
		memfree(utf8string);
#else
		do {
			int mnbytes = XmbLookupString(xic, xkeyevent, xmbstring, xmblen - 1, &keysym_unicode, &status);
			xmbstring[mnbytes] = '\0';
			if (status == XBufferOverflow) {
				xmblen = mnbytes + 1;
				xmbstring = (char *)memrealloc(xmbstring, xmblen);
			}
		} while (status == XBufferOverflow);
#endif
#ifdef XKB_ENABLED
	} else if (xkeyevent->type == KeyPress && wd.xkb_state && xkb_loaded_v05p) {
		xkb_compose_feed_result res = xkb_compose_state_feed(wd.xkb_state, keysym_unicode);
		if (res == XKB_COMPOSE_FEED_ACCEPTED) {
			if (xkb_compose_state_get_status(wd.xkb_state) == XKB_COMPOSE_COMPOSED) {
				bool keypress = xkeyevent->type == KeyPress;
				Key keycode = KeyMappingX11::get_keycode(keysym_keycode);
				Key physical_keycode = KeyMappingX11::get_scancode(xkeyevent->keycode);
				if (keycode >= Key::A + 32 && keycode <= Key::Z + 32) {
					keycode -= 'a' - 'A';
				}