<!-- Describe the issue -->
`getrawtransaction` fails
<!--- What behavior did you expect? -->
Return decoded raw tx
<!--- What was the actual behavior (provide screenshots if the issue is GUI-related)? -->
* `bitcoin-qt -prune=8192  -server -rpcuser=rpc -rpcpassword=rpc -onlynet=ipv4 -rpcbind=127.0.0.1:18332 -testnet`
  * BTC 0.18.0
  * `getrawtransaction b423b2b22d6d74376de2887c07f7c84ae890a93d541fcc6dbf3686f2923b2753 1`
![image](https://user-images.githubusercontent.com/3670331/58841021-658d7180-8668-11e9-9f9f-ed1f794070ea.png)
  * BTC 0.17.1
  * `getrawtransaction b423b2b22d6d74376de2887c07f7c84ae890a93d541fcc6dbf3686f2923b2753 1`
![image](https://user-images.githubusercontent.com/3670331/58841089-9ff70e80-8668-11e9-8a68-5022631b43d7.png)

<!--- How reliably can you reproduce the issue, what are the steps to do so? -->
Request `getrawtransaction`.
<!-- What version of Bitcoin Core are you using, where did you get it (website, self-compiled, etc)? -->
Official from site.
<!-- What type of machine are you observing the error on (OS/CPU and disk type)? -->
`Linux pentagon 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u2 (2019-05-13) x86_64 GNU/Linux`, u5200, 2x8Gb, SSD
<!-- For the GUI-related issue on Linux provide names and versions of a distro, a desktop environment and a graphical shell (if relevant). -->
QT
<!-- Any extra information that might be useful in the debugging process. -->
<!--- This is normally the contents of a `debug.log` or `config.log` file. Raw text or a link to a pastebin type site are preferred. -->

},
                RPCExamples{
                    HelpExampleCli("combinepsbt", "[\"mybase64_1\", \"mybase64_2\", \"mybase64_3\"]")
                },
            }.ToString());
    RPCTypeCheck(request.params, {UniValue::VARR}, true);
    
    std::vector<PartiallySignedTransaction> psbtxs;
    UniValue txs = request.params[0].get_array();
    if (txs.empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Parameter 'txs' cannot be empty");
    }
    for (unsigned int i = 0; i < txs.size(); ++i) {
        PartiallySignedTransaction psbtx;
        std::string error;
        if (!DecodeBase64PSBT(psbtx, txs[i].get_str(), error)) {
            throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
        }
        psbtxs.push_back(psbtx);
    }
    PartiallySignedTransaction merged_psbt;
    const TransactionError error = CombinePSBTs(merged_psbt, psbtxs);
    if (error != TransactionError::OK) {
        throw JSONRPCTransactionError(error);
    }
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << merged_psbt;
    return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
}
UniValue finalizepsbt(const JSONRPCRequest& request)