
<!-- Describe the issue -->
Following commit 46004790588c24174a0bec49b540d158ce163ffd (@achow101), `decodepsbt` overstates the fee, apparently including both the `witness_utxo` and `non_witness_utxo` amounts in the inputs.

**Expected behavior**

The decoded fee should be the sum of the inputs, minus the sum of the outputs.

**Actual behavior**

The decoded fee is exactly twice the amount of the inputs, minus the sum of the outputs.

**To reproduce**

Build any PSBT using `createpsbt`, `walletprocesspsbt`, then decode it with `decodepsbt`. See the `fee` field in the JSON.

**System information**

I compiled myself from 5550fa5983ea59e7ccef6540b7ec49a1770fb3ca on Whonix 14.

Then I did `git revert 46004790588c24174a0bec49b540d158ce163ffd ` and the problem went away.

view.SetBackend(viewMempool); 
        for (const CTxIn& txin : psbtx.tx->vin) {
            view.AccessCoin(txin.prevout); 
        }
        view.SetBackend(viewDummy); 
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
        PSBTInput& input = psbtx.inputs.at(i);
        if (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
            continue;
        }
        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
        if (IsSegWitOutput(provider, coin.out.scriptPubKey)) {
            input.witness_utxo = coin.out;
        }
        
        
        
        SignPSBTInput(public_provider, psbtx, i,  1);
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
        UpdatePSBTOutput(public_provider, psbtx, i);
    }
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
}
UniValue joinpsbts(const JSONRPCRequest& request)