### 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)

Atom client_list_prop = XInternAtom(x11_display, "_NET_CLIENT_LIST", True);
		if (client_list_prop != None) {
			unsigned long clients_len = 0;
			unsigned char *clients_data = nullptr;
			if (XGetWindowProperty(x11_display, x11_window, client_list_prop, 0, LONG_MAX, False, XA_WINDOW, &type, &format, &clients_len, &remaining, &clients_data) == Success) {
				if ((format == 32) && (clients_len > 0) && clients_data) {
					Window *windows_data = (Window *)clients_data;
					Rect2i desktop_rect;
					bool desktop_valid = false;
					
					{
						Atom desktop_geometry_prop = XInternAtom(x11_display, "_NET_DESKTOP_GEOMETRY", True);
						if (desktop_geometry_prop != None) {
							unsigned long geom_len = 0;
							unsigned char *geom_data = nullptr;
							if (XGetWindowProperty(x11_display, x11_window, desktop_geometry_prop, 0, LONG_MAX, False, XA_CARDINAL, &type, &format, &geom_len, &remaining, &geom_data) == Success) {
								if ((format == 32) && (geom_len >= 2) && geom_data) {
									desktop_valid = true;
									long *size_data = (long *)geom_data;
									desktop_rect.size.x = size_data[0];
									desktop_rect.size.y = size_data[1];
								}
							}
							if (geom_data) {
								XFree(geom_data);
							}
						}
					}