fix: disk is also virtual if product is None

Example on QEMU/KVM:

```json
{'logicalname': '/dev/vda', 'product': None, 'serial': None, 'version': None, 'size': 10737418240, 'description': 'Virtual I/O device', 'type': 'Virtual I/O device'}
```

netbox_agent/inventory.py

@@ -309,7 +309,7 @@ class Inventory():
         description = disk.get('description')
         size = disk.get('size')
         product = disk.get('product')
-        if logicalname in raid_devices or disk_type is None:
+        if logicalname in raid_devices or disk_type is None or product is None:
             return True
         non_raid_disks = [
             'MR9361-8i',