cs: set missing_validators(_power) metrics to 0 for 1st block

also, do not send any LastCommitInfo.Votes for 1st block.

remember that the first LastCommit is intentionally empty, so it makes
sense for LastCommitInfo.Votes to also be empty. Because we can't really
tell if validator signed or not. Similar for ^ metrics, we can't say if
particular validator was missing or not.

Closes #4192

consensus/state.go

@@ -1461,20 +1461,26 @@ func (cs *ConsensusState) finalizeCommit(height int64) {
 func (cs *ConsensusState) recordMetrics(height int64, block *types.Block) {
 	cs.metrics.Validators.Set(float64(cs.Validators.Size()))
 	cs.metrics.ValidatorsPower.Set(float64(cs.Validators.TotalVotingPower()))
-	missingValidators := 0
-	missingValidatorsPower := int64(0)
-	for i, val := range cs.Validators.Validators {
-		if i >= len(block.LastCommit.Signatures) {
-			break
-		}
-		commitSig := block.LastCommit.Signatures[i]
-		if commitSig.Absent() {
-			missingValidators++
-			missingValidatorsPower += val.VotingPower
+
+	var (
+		missingValidators      int
+		missingValidatorsPower int64
+	)
+	// height=0 -> MissingValidators and MissingValidatorsPower are both 0.
+	// Remember that the first LastCommit is intentionally empty, so it's not
+	// fair to increment missing validators number.
+	if height > 1 {
+		for i, val := range cs.Validators.Validators {
+			commitSig := block.LastCommit.Signatures[i]
+			if commitSig.Absent() {
+				missingValidators++
+				missingValidatorsPower += val.VotingPower
+			}
 		}
 	}
 	cs.metrics.MissingValidators.Set(float64(missingValidators))
 	cs.metrics.MissingValidatorsPower.Set(float64(missingValidatorsPower))
+
 	cs.metrics.ByzantineValidators.Set(float64(len(block.Evidence.Evidence)))
 	byzantineValidatorsPower := int64(0)
 	for _, ev := range block.Evidence.Evidence {

state/execution.go

@@ -332,16 +332,17 @@ func getBeginBlockValidatorInfo(block *types.Block, stateDB dbm.DB) (abci.LastCo
 		lastValSet = types.NewValidatorSet(nil)
 	}
 
-	for i, val := range lastValSet.Validators {
-		if i >= len(block.LastCommit.Signatures) {
-			break
-		}
-		commitSig := block.LastCommit.Signatures[i]
-		voteInfo := abci.VoteInfo{
-			Validator:       types.TM2PB.Validator(val),
-			SignedLastBlock: !commitSig.Absent(),
+	// block.Height=1 -> LastCommitInfo.Votes are empty.
+	// Remember that the first LastCommit is intentionally empty, so it makes
+	// sense for LastCommitInfo.Votes to also be empty.
+	if block.Height > 1 {
+		for i, val := range lastValSet.Validators {
+				commitSig := block.LastCommit.Signatures[i]
+				voteInfos[i] = abci.VoteInfo{
+					Validator:       types.TM2PB.Validator(val),
+					SignedLastBlock: !commitSig.Absent(),
+				}
 		}
-		voteInfos[i] = voteInfo
 	}
 
 	for i, ev := range block.Evidence.Evidence {