ASN Lookup expert: Missing sane default value for database path

[sebix]

https://github.com/certtools/intelmq/blob/adb2d156d642ea4b804e26b12e81d1b0d21ec425/intelmq/bots/experts/asn_lookup/expert.py#L28

I suggest that the default path is /var/lib/intelmq/bots/asn_lookup/ipasn.dat as was the case some time ago.

Also, the update script could check first if the path exists (and isn't a None or empty string) and even if it is writeable before downloading the data.

[sebix]

Also, the update script could check first if the path exists (and isn't a None or empty string) and even if it is writeable before downloading the data.

And it isn't a directory. The documentation is not clear either.