When viewing Realtime graphs, undefined variable errors may be reported

Hi Guys,

i see this error during realtime graphs:
```
2023-06-08 10:45:35 - PHP ERROR WARNING Backtrace: (/graph_realtime.php[245]:CactiErrorHandler())
2023-06-08 10:45:35 - ERROR PHP WARNING: Undefined variable $rra_id in file: /var/www/html/cacti/graph_realtime.php on line: 245
```

PHP: 8.1.5

thanks a lot. stefano.