### 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)

KeySym keysym_unicode_nm = 0; 
		XLookupString(&xkeyevent_no_mod, nullptr, 0, &keysym_unicode_nm, nullptr);
		keysym = String::chr(xkb_keysym_to_utf32(xkb_keysym_to_upper(keysym_unicode_nm)));
	}
#endif
	
	if (!xmbstring) {
		
		xmbstring = (char *)memalloc(sizeof(char) * 8);
		xmblen = 8;
	}
	if (xkeyevent->type == KeyPress && wd.xic) {
		Status status;
#ifdef X_HAVE_UTF8_STRING
		int utf8len = 8;
		char *utf8string = (char *)memalloc(sizeof(char) * utf8len);
		int utf8bytes = Xutf8LookupString(wd.xic, xkeyevent, utf8string,
				utf8len - 1, &keysym_unicode, &status);
		if (status == XBufferOverflow) {
			utf8len = utf8bytes + 1;
			utf8string = (char *)memrealloc(utf8string, utf8len);
			utf8bytes = Xutf8LookupString(wd.xic, xkeyevent, utf8string,
					utf8len - 1, &keysym_unicode, &status);
		}
		utf8string[utf8bytes] = '\0';
		if (status == XLookupChars) {
			bool keypress = xkeyevent->type == KeyPress;
			Key keycode = KeyMappingX11::get_keycode(keysym_keycode);
			Key physical_keycode = KeyMappingX11::get_scancode(xkeyevent->keycode);
			if (keycode >= Key::A + 32 && keycode <= Key::Z + 32) {