extractPack should throw an error when no pack data is found

[ryanwalder]

When passing a src directory that does not contain valid LevelDB data extractPack should throw an error.

Example:

import { compilePack, extractPack } from "@foundryvtt/foundryvtt-cli";

extractPack("path/to/dir/without/leveldb/data", "output")

This does not throw an error as you would expect but will create the output directory.