We do [check that it's not lower than shard check frequency](https://github.com/snowplow-devops/kinsumer/blob/4e194156cd72b3d6e6bc82518e0c3a99f39825be/config.go#L169-L171) - which can't be 0. So we will get an error in this case, but we should check directly that it's not 0 and throw a specific error for that case too.