fix(sequencer): update put_price_for_currency_pair

[noot]

Summary

update put_price_for_currency_pair to error if state is not found. this is correct as the function is only called from apply_prices_from_vote_extensions, which only contains currency pairs that are already in the app state, as an invariant of the id_to_currency_pair validation done inside validate_id_to_currency_pair_mapping. thus, the previous else case where the state didn't exist would never be hit.

Background

resolves oracle audit issue 3.1.

Changes

• update put_price_for_currency_pair to error if state is not found.

Testing

existing unit tests