chainntnfs: stop lnd when received witness stack is empty

This commit uses `Criticalf` to gracefully stop `lnd` when the received
witness data is empty.

chainntnfs/mempool.go

@@ -223,12 +223,20 @@ func (m *MempoolNotifier) findRelevantInputs(tx *btcutil.Tx) (inputsWithTx,
 		}
 		watchedInputs[*op] = details
 
+		// Sanity check the witness stack. If it's not empty, continue
+		// to next iteration.
+		if details.HasSpenderWitness() {
+			continue
+		}
+
 		// Return an error if the witness data is not present in the
 		// spending transaction.
-		if !details.HasSpenderWitness() {
+		Log.Criticalf("Found spending tx for outpoint=%v in mempool, "+
+			"but the transaction %v does not have witness",
+			op, details.SpendingTx.TxHash())
+
 		return nil, ErrEmptyWitnessStack
 	}
-	}
 
 	return watchedInputs, nil
 }

chainntnfs/txnotifier.go

@@ -1305,10 +1305,13 @@ func (n *TxNotifier) updateSpendDetails(spendRequest SpendRequest,
 	// Return an error if the witness data is not present in the spending
 	// transaction.
 	//
-	// TODO(yy): maybe we should do a panic here instead to inform the user
+	// NOTE: if the witness stack is empty, we will do a critical log which
-	// to reindex the bitcoind since it's critical error?
+	// shuts down the node.
-	// panic("Please re-index your bitcoind...")
 	if !details.HasSpenderWitness() {
+		Log.Criticalf("Found spending tx for outpoint=%v, but the "+
+			"transaction %v does not have witness",
+			spendRequest.OutPoint, details.SpendingTx.TxHash())
+
 		return ErrEmptyWitnessStack
 	}