<!-- 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. -->

{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
        throw std::runtime_error(
            RPCHelpMan{"finalizepsbt",
                "Finalize the inputs of a PSBT. If the transaction is fully signed, it will produce a\n"
                "network serialized transaction which can be broadcast with sendrawtransaction. Otherwise a PSBT will be\n"
                "created which has the final_scriptSig and final_scriptWitness fields filled for inputs that are complete.\n"
                "Implements the Finalizer and Extractor roles.\n",
                {
                    {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"},
                    {"extract", RPCArg::Type::BOOL,  "true", "If true and the transaction is complete,\n"
            "                             extract and return the complete transaction in normal network serialization instead of the PSBT."},
                },
                RPCResult{
            "{\n"
            "  \"psbt\" : \"value\",          (string) The base64-encoded partially signed transaction if not extracted\n"
            "  \"hex\" : \"value\",           (string) The hex-encoded network transaction if extracted\n"
            "  \"complete\" : true|false,   (boolean) If the transaction has a complete set of signatures\n"
            "  ]\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("finalizepsbt", "\"psbt\"")
                },
            }.ToString());
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL}, true);
    
    PartiallySignedTransaction psbtx;
    std::string error;
    if (!DecodeBase64PSBT(psbtx, request.params[0].get_str(), error)) {