### 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)

r_error = ERR_UNAVAILABLE;
		ERR_FAIL_MSG("Can't load Xext dynamically.");
	}
	if (initialize_xinerama(dylibloader_verbose) != 0) {
		r_error = ERR_UNAVAILABLE;
		ERR_FAIL_MSG("Can't load Xinerama dynamically.");
	}
	if (initialize_xrandr(dylibloader_verbose) != 0) {
		r_error = ERR_UNAVAILABLE;
		ERR_FAIL_MSG("Can't load Xrandr dynamically.");
	}
	if (initialize_xrender(dylibloader_verbose) != 0) {
		r_error = ERR_UNAVAILABLE;
		ERR_FAIL_MSG("Can't load Xrender dynamically.");
	}
	if (initialize_xinput2(dylibloader_verbose) != 0) {
		r_error = ERR_UNAVAILABLE;
		ERR_FAIL_MSG("Can't load Xinput2 dynamically.");
	}
#else
#ifdef XKB_ENABLED
	xkb_loaded = true;
#endif
#endif
#ifdef XKB_ENABLED
	if (xkb_loaded) {
		xkb_ctx = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
		if (xkb_ctx) {
			const char *locale = getenv("LC_ALL");
			if (!locale || !*locale) {