### 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_
	ERR_FAIL_COND(p_window == p_parent);
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd_window = windows[p_window];
	WindowID prev_parent = wd_window.transient_parent;
	ERR_FAIL_COND(prev_parent == p_parent);
	DEBUG_LOG_X11("window_set_transient: %lu (%u), prev_parent=%u, parent=%u\n", wd_window.x11_window, p_window, prev_parent, p_parent);
	ERR_FAIL_COND_MSG(wd_window.on_top, "Windows with the 'on top' can't become transient.");
	if (p_parent == INVALID_WINDOW_ID) {
		
		ERR_FAIL_COND(prev_parent == INVALID_WINDOW_ID);
		ERR_FAIL_COND(!windows.has(prev_parent));
		WindowData &wd_parent = windows[prev_parent];
		wd_window.transient_parent = INVALID_WINDOW_ID;
		wd_parent.transient_children.erase(p_window);
		XSetTransientForHint(x11_display, wd_window.x11_window, None);
		XWindowAttributes xwa;
		XSync(x11_display, False);