accounts/abi/bind/backends: make suggestGasPrice compatible with non-1559 chains (ethereum#23840)

Author: MariusVanDerWijden

accounts/abi/bind/backends/simulated.go

@@ -462,7 +462,10 @@ func (b *SimulatedBackend) PendingNonceAt(ctx context.Context, account common.Ad
 // SuggestGasPrice implements ContractTransactor.SuggestGasPrice. Since the simulated
 // chain doesn't have miners, we just return a gas price of 1 for any call.
 func (b *SimulatedBackend) SuggestGasPrice(ctx context.Context) (*big.Int, error) {
-	return b.pendingBlock.Header().BaseFee, nil
+	if b.pendingBlock.Header().BaseFee != nil {
+		return b.pendingBlock.Header().BaseFee, nil
+	}
+	return big.NewInt(1), nil
 }
 
 // SuggestGasTipCap implements ContractTransactor.SuggestGasTipCap. Since the simulated