`ScanForWalletTransactions()` has the following comment about its return value:

```
 * Returns null if scan was successful. Otherwise, if a complete rescan was not
 * possible (due to pruning or corruption), returns pointer to the most recent
 * block that could not be scanned.
```

This is not strictly true. If `abortrescan` is called, then `ScanForWalletTransactions()` will return `nullptr`, even though the scan wasn't successful to the tip.

This in turn causes a minor bug in `importmulti`, where the call doesn't return the correct error and warning about potentially not finding transactions if `abortrescan` was called.

I think the correct fix is for `ScanForWalletTransactions()` to inform the caller that the rescan was aborted.
"\nResult:\n"
            "{\n"
            "  \"psbt\" : \"value\",          (string) The base64-encoded partially signed transaction\n"
            "  \"complete\" : true|false,   (boolean) If the transaction has a complete set of signatures\n"
            "  ]\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("walletprocesspsbt", "\"psbt\"")
        );
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL, UniValue::VSTR});
    
    PartiallySignedTransaction psbtx;
    std::string error;
    if (!DecodePSBT(psbtx, request.params[0].get_str(), error)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
    }
    
    int nHashType = ParseSighashString(request.params[2]);
    
    bool sign = request.params[1].isNull() ? true : request.params[1].get_bool();
    bool bip32derivs = request.params[3].isNull() ? false : request.params[3].get_bool();
    bool complete = FillPSBT(pwallet, psbtx, nHashType, sign, bip32derivs);
    UniValue result(UniValue::VOBJ);
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    result.pushKV("psbt", EncodeBase64(ssTx.str()));
    result.pushKV("complete", complete);
    return result;
}
UniValue walletcreatefundedpsbt(const JSONRPCRequest& request)