### 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)

char str_xkb[256] = {};
				int str_xkb_size = xkb_compose_state_get_utf8(wd.xkb_state, str_xkb, 255);
				String tmp;
				tmp.parse_utf8(str_xkb, str_xkb_size);
				for (int i = 0; i < tmp.length(); i++) {
					Ref<InputEventKey> k;
					k.instantiate();
					if (physical_keycode == Key::NONE && keycode == Key::NONE && tmp[i] == 0) {
						continue;
					}
					if (keycode == Key::NONE) {
						keycode = (Key)physical_keycode;
					}
					_get_key_modifier_state(xkeyevent->state, k);
					k->set_window_id(p_window);
					k->set_pressed(keypress);
					k->set_keycode(keycode);
					k->set_physical_keycode(physical_keycode);
					if (!keysym.is_empty()) {
						k->set_key_label(fix_key_label(keysym[0], keycode));
					} else {
						k->set_key_label(keycode);
					}
					if (keypress) {
						k->set_unicode(fix_unicode(tmp[i]));
					}
					k->set_echo(false);
					if (k->get_keycode() == Key::BACKTAB) {
						
						k->set_keycode(Key::TAB);