lookup.py does not return correct results for ASN

Looking up by ASN doesn't seem to work, though I can look up a valid prefix that is announced by 19281 and that shows up correctly in a search, so the MMDB file has the data.

```
(.venv) root@mmdbpython:/home/jtodd/mrt2mmdb/mrt2mmdb# ./lookup.py --mmdb ../../GeoIP2-Enterprise_20241018/GeoIP2-Enterprise.mmdb.trim1 --asn 19281
ASN not found
ASN not found
<this continues forever>
```