### 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)

err = dlerror();
		
		
		xrandr_handle = dlopen("libXrandr.so.3", RTLD_LAZY);
		if (!xrandr_handle) {
			fprintf(stderr, "could not load libXrandr.so.2, Error: %s\n", err);
		}
	} else {
		XRRQueryVersion(x11_display, &xrandr_major, &xrandr_minor);
		if (((xrandr_major << 8) | xrandr_minor) >= 0x0105) {
			xrr_get_monitors = (xrr_get_monitors_t)dlsym(xrandr_handle, "XRRGetMonitors");
			if (!xrr_get_monitors) {
				err = dlerror();
				fprintf(stderr, "could not find symbol XRRGetMonitors\nError: %s\n", err);
			} else {
				xrr_free_monitors = (xrr_free_monitors_t)dlsym(xrandr_handle, "XRRFreeMonitors");
				if (!xrr_free_monitors) {
					err = dlerror();
					fprintf(stderr, "could not find XRRFreeMonitors\nError: %s\n", err);
					xrr_get_monitors = nullptr;
				}
			}
		}
	}
	if (!_refresh_device_info()) {
		OS::get_singleton()->alert("Your system does not support XInput 2.\n"
								   "Please upgrade your distribution.",
				"Unable to initialize XInput");
		r_error = ERR_UNAVAILABLE;
		return;