### 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)

}
	}
	mouse_mode = p_mode;
	if (mouse_mode == MOUSE_MODE_CAPTURED || mouse_mode == MOUSE_MODE_CONFINED || mouse_mode == MOUSE_MODE_CONFINED_HIDDEN) {
		
		_flush_mouse_motion();
		WindowID window_id = _get_focused_window_or_popup();
		if (!windows.has(window_id)) {
			window_id = MAIN_WINDOW_ID;
		}
		WindowData &window = windows[window_id];
		if (XGrabPointer(
					x11_display, window.x11_window, True,
					ButtonPressMask | ButtonReleaseMask | PointerMotionMask,
					GrabModeAsync, GrabModeAsync, window.x11_window, None, CurrentTime) != GrabSuccess) {
			ERR_PRINT("NO GRAB");
		}
		if (mouse_mode == MOUSE_MODE_CAPTURED) {
			center.x = window.size.width / 2;
			center.y = window.size.height / 2;
			XWarpPointer(x11_display, None, window.x11_window,
					0, 0, 0, 0, (int)center.x, (int)center.y);
			Input::get_singleton()->set_mouse_position(center);
		}
	} else {
		do_mouse_warp = false;
	}
	XFlush(x11_display);
}
DisplayServerX11::MouseMode DisplayServerX11::mouse_get_mode() const {