[viewchange] should not startNewView is not in viewChange mode

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

consensus/view_change.go

@@ -278,9 +278,17 @@ func (consensus *Consensus) startNewView(viewID uint64, newLeaderPriKey *bls.Pri
 	consensus.mutex.Lock()
 	defer consensus.mutex.Unlock()
 
+	if !consensus.IsViewChangingMode() {
+		return errors.New("not in view changing mode anymore")
+	}
+
 	msgToSend := consensus.constructNewViewMessage(
 		viewID, newLeaderPriKey,
 	)
+	if msgToSend == nil {
+		return errors.New("failed to construct NewView message")
+	}
+
 	if err := consensus.msgSender.SendWithRetry(
 		consensus.blockNum,
 		msg_pb.MessageType_NEWVIEW,

consensus/view_change_msg.go

@@ -118,6 +118,9 @@ func (consensus *Consensus) constructNewViewMessage(viewID uint64, priKey *bls.P
 	vcMsg.Payload, vcMsg.PreparedBlock = consensus.vc.GetPreparedBlock(consensus.FBFTLog, consensus.blockHash)
 	vcMsg.M2Aggsigs, vcMsg.M2Bitmap = consensus.vc.GetM2Bitmap(viewID)
 	vcMsg.M3Aggsigs, vcMsg.M3Bitmap = consensus.vc.GetM3Bitmap(viewID)
+	if vcMsg.M3Bitmap == nil || vcMsg.M3Aggsigs == nil {
+		return nil
+	}
 
 	marshaledMessage, err := consensus.signAndMarshalConsensusMessage(message, priKey.Pri)
 	if err != nil {