### 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)

for (const KeyValue<WindowID, WindowData> &E : windows) {
						const WindowData &wd_other = E.value;
						if (wd_other.focused) {
							int x, y;
							Window child;
							XTranslateCoordinates(x11_display, wd.x11_window, wd_other.x11_window, event.xmotion.x, event.xmotion.y, &x, &y, &child);
							Point2i pos_focused(x, y);
							mm->set_window_id(E.key);
							mm->set_position(pos_focused);
							mm->set_global_position(pos_focused);
							mm->set_velocity(Input::get_singleton()->get_last_mouse_velocity());
							Input::get_singleton()->parse_input_event(mm);
							break;
						}
					}
				}
			} break;
			case KeyPress:
			case KeyRelease: {
				if (ignore_events) {
					break;
				}
#ifdef DISPLAY_SERVER_X11_DEBUG_LOGS_ENABLED
				if (event.type == KeyPress) {
					DEBUG_LOG_X11("[%u] KeyPress window=%lu (%u), keycode=%u, time=%lu \n", frame, event.xkey.window, window_id, event.xkey.keycode, event.xkey.time);
				} else {
					DEBUG_LOG_X11("[%u] KeyRelease window=%lu (%u), keycode=%u, time=%lu \n", frame, event.xkey.window, window_id, event.xkey.keycode, event.xkey.time);