Steps to reproduce:

* Build with `integer` sanitizer
* `UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./src/qt/bitcoin-qt`
* Enter into the RPC debug console: `decodepsbt "cHNidP8BAKOro2MDAwMDA5ggCAAA////CQAtAAD+///1AAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJAAAAAAAAAAAAAAAAAAAAAAAAAD+///1Zm9ybmV3nWx1Y2vmelLmegAAAAAAAAAAAAAAAAAAAAMKAwMDAwMDAwMDAwMACvMBA3FkAAAAAAAAAAAABAAlAAAAAAAAACEWDQ0zDQ0NDQ0NDQ0NCwEAAH9/f39/fwMAAABNo6P///kAAA=="`
{
                    PSBTProprietary this_prop;
                    skey >> this_prop.identifier;
                    this_prop.subtype = ReadCompactSize(skey);
                    this_prop.key = key;
                    if (m_proprietary.count(this_prop) > 0) {
                        throw std::ios_base::failure("Duplicate Key, proprietary key already found");
                    }
                    s >> this_prop.value;
                    m_proprietary.insert(this_prop);
                    break;
                }
                
                default:
                    if (unknown.count(key) > 0) {
                        throw std::ios_base::failure("Duplicate Key, key for unknown value already provided");
                    }
                    
                    std::vector<unsigned char> val_bytes;
                    s >> val_bytes;
                    unknown.emplace(std::move(key), std::move(val_bytes));
                    break;
            }
        }
        if (!found_sep) {
            throw std::ios_base::failure("Separator is missing at the end of an input map");
        }
    }
    template <typename Stream>
    PSBTInput(deserialize_type, Stream& s) {