Node Cleanup include nodes with no "Last Seen Date"

[HoleInTheSeat]

When using the Scheduled Node Cleanup maintenance task, device that have a last seen date of 0000-00-00 00:00:00 are not affected.

Having the cleanup include devices without a last seen date would help to better clean up the DB

I was able to manually mass delete them via MariaDB

MariaDB [pf]> SELECT mac, last_seen  FROM node  WHERE last_seen < '2024-09-30';
+-------------------+---------------------+
| mac               | last_seen           |
+-------------------+---------------------+
| 00:02:c2:8a:76:13 | 0000-00-00 00:00:00 |
| 00:02:c3:8b:b4:78 | 0000-00-00 00:00:00 |
| 00:02:c3:8b:4b:55 | 0000-00-00 00:00:00 |
...