core: don't cache zero nonce in txNoncer (#25603)

This changes the nonce cache used by TxPool to not store cached
nonces for non-existing accounts.

core/tx_noncer.go

@@ -49,7 +49,9 @@ func (txn *txNoncer) get(addr common.Address) uint64 {
 	defer txn.lock.Unlock()
 
 	if _, ok := txn.nonces[addr]; !ok {
-		txn.nonces[addr] = txn.fallback.GetNonce(addr)
+		if nonce := txn.fallback.GetNonce(addr); nonce != 0 {
+			txn.nonces[addr] = nonce
+		}
 	}
 	return txn.nonces[addr]
 }
@@ -70,7 +72,9 @@ func (txn *txNoncer) setIfLower(addr common.Address, nonce uint64) {
 	defer txn.lock.Unlock()
 
 	if _, ok := txn.nonces[addr]; !ok {
-		txn.nonces[addr] = txn.fallback.GetNonce(addr)
+		if nonce := txn.fallback.GetNonce(addr); nonce != 0 {
+			txn.nonces[addr] = nonce
+		}
 	}
 	if txn.nonces[addr] <= nonce {
 		return

core/tx_pool.go

@@ -463,9 +463,6 @@ func (pool *TxPool) SetGasPrice(price *big.Int) {
 // Nonce returns the next nonce of an account, with all transactions executable
 // by the pool already applied on top.
 func (pool *TxPool) Nonce(addr common.Address) uint64 {
-	pool.mu.RLock()
-	defer pool.mu.RUnlock()
-
 	return pool.pendingNonces.get(addr)
 }