Partial Set Security: Drop chain proposals with empty validator set at spawn time

[insumity]

Problem

Consider a consumer addition proposal for an Opt In chain chainID that is voted on but no validator opts in during the voting period. The generated consumer genesis file would have any empty validator set. So, the chain won't be able to start. Nevertheless we still store data about chainID such as denylists, etc. This means that no chain with chainID will be able to be voted upon unless chainID gets first removed.

Closing criteria

If a chain ends up with a genesis that has an empty validator set, we should just drop the proposal and not store anything in regards to this chain.

Thanks to @dasanchez for finding this out!