Fix and unit-test condition vote.Height < 0 in Vote::ValidateBasic in v0.37.x and v0.34.x
PRs:

• Add UT (it's passing as the problem no longer exists) on feature/abci++vef
  • Votes can't have zero height #511
• Add failing UT, then fix on v0.37.x
  • Votes can't have zero height #512
• Add failing UT, then fix on v0.34.x
  • Votes can't have zero height #513

For context, check where this is coming from.