bugfix: only fetch AddressLesserGreater when validator is eligible

[eelanagaraj]

Description

This Bug is likely caused by an error in VoteMetadata when revoking votes for an ineligible validator, and would be triggered by anything calling RevokeMetadata (which in turn calls VoteMetadata), so any of the preprocessRevoke funcs (RevokeActiveVotes, RevokePendingVotes in Election.sol; ReleaseGoldRevokePendingVotes, ReleaseGoldRevokeActiveVotes which just call the Election.sol version from ReleaseGold.sol).

Election.sol revoke functions require passing in the (lesser, greater) addresses (prev/next addresses in the linked list storing the eligible validators, votes.total.eligible, which crucially excludes ineligible validators). In cases like this one, where validators are not eligible but have votes, the revoke functions simply ignore the lesser/greater addresses and don't update the linked list (since ineligible addresses are excluded).

Normal cases need to still find the (lesser, greater) addresses in the linked list of eligible validators, but in cases of ineligible validators, we can set (lesser, greater) to 0 (or anything else. -- Tested this against Election.sol directly).

Locally running Rosetta with this version of kliento looks like it fixes this issue.

Tested

• Confirmed assumptions against Election.sol in the monorepo (adding protocol tests; will put up a PR for this)
• Manually reproduced the error described in the issue (as best as possible, by hard-coding certain function returns -- couldn't get around this without a synced Rosetta node)
• Manually tested locally and it seems to fix the error ^
• Should be tested more extensively to be considered production ready

[palango]

Looks good to me! Thanks for fixing it so quickly!