[epoch] fix IsLastBlock if block is less than epoch block

Signed-off-by: Leo Chen <leo@harmony.one>

core/blockchain.go

@@ -224,6 +224,7 @@ func (bc *BlockChain) ValidateNewBlock(block *types.Block) error {
 }
 
 // IsEpochBlock returns whether this block is the first block of an epoch.
+// TODO: lc this is not used
 func IsEpochBlock(block *types.Block) bool {
 	return block.NumberU64()%ShardingSchedule.BlocksPerEpoch() == 0
 }

internal/configs/sharding/localnet.go

@@ -48,6 +48,8 @@ func (ls localnetSchedule) CalcEpochNumber(blockNum uint64) *big.Int {
 func (ls localnetSchedule) IsLastBlock(blockNum uint64) bool {
 	blocks := ls.BlocksPerEpoch()
 	switch {
+	case blockNum < localnetEpochBlock1-1:
+		return false
 	case blockNum == localnetEpochBlock1-1:
 		return true
 	default:

internal/configs/sharding/mainnet.go

@@ -44,6 +44,8 @@ func (ms mainnetSchedule) CalcEpochNumber(blockNum uint64) *big.Int {
 func (ms mainnetSchedule) IsLastBlock(blockNum uint64) bool {
 	blocks := ms.BlocksPerEpoch()
 	switch {
+	case blockNum < mainnetEpochBlock1-1:
+		return false
 	case blockNum == mainnetEpochBlock1-1:
 		return true
 	default:

internal/configs/sharding/testnet.go

@@ -49,6 +49,8 @@ func (ts testnetSchedule) CalcEpochNumber(blockNum uint64) *big.Int {
 func (ts testnetSchedule) IsLastBlock(blockNum uint64) bool {
 	blocks := ts.BlocksPerEpoch()
 	switch {
+	case blockNum < testnetEpochBlock1-1:
+		return false
 	case blockNum == testnetEpochBlock1-1:
 		return true
 	default: