### 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)

Rect2i rect = _screen_get_rect(p_screen);
	
	
	int x11_screen_count = ScreenCount(x11_display);
	Window x11_window = RootWindow(x11_display, p_screen < x11_screen_count ? p_screen : 0);
	Atom type;
	int format = 0;
	unsigned long remaining = 0;
	
	unsigned int desktop_index = 0;
	Atom desktop_prop = XInternAtom(x11_display, "_NET_CURRENT_DESKTOP", True);
	if (desktop_prop != None) {
		unsigned long desktop_len = 0;
		unsigned char *desktop_data = nullptr;
		if (XGetWindowProperty(x11_display, x11_window, desktop_prop, 0, LONG_MAX, False, XA_CARDINAL, &type, &format, &desktop_len, &remaining, &desktop_data) == Success) {
			if ((format == 32) && (desktop_len > 0) && desktop_data) {
				desktop_index = (unsigned int)desktop_data[0];
			}
			if (desktop_data) {
				XFree(desktop_data);
			}
		}
	}
	bool use_simple_method = true;
	
	if (is_multiscreen) {
		
		Atom gtk_workareas_prop = XInternAtom(x11_display, "_GTK_WORKAREAS", False);
		if (gtk_workareas_prop != None) {