buffer reading position is wrong when reading string data with code points beyond U+007F

template<>
QString QMqttConnection::readBufferTyped()
{
    const quint16 size = readBufferTyped<quint16>();
    return QString::fromUtf8(reinterpret_cast<const char *>(readBuffer(size).constData()), size);
}

        case 0x26: { // 3.15.2.2.5 User property
            ...
            const QString propertyValue = readBufferTyped<QString>();
            propertyLength -= propertyValue.length() + 2;

    template<class T>
    T QMqttConnection::readBufferTyped(int *remainingLen = nullptr);

  ...
    template<>
    quint16 QMqttConnection::readBufferTyped(int *remainingLen = nullptr)
   {
         const quint16 result =  qFromBigEndian<quint16>(reinterpret_cast<const quint16 *>(readBuffer(2).constData()));
        if (remainingLen)
            *remainingLen -= 2;
         return result;
    }

    ...
     
    template<>
    QString QMqttConnection::readBufferTyped(int *remainingLen = nullptr)
    {
        const quint16 size = readBufferTyped<quint16>(remainingLen);
        const QByteArray ba = reinterpret_cast<const char *>(readBuffer(size).constData()), size);
        if (remainingLen)
            *remainingLen -= ba.size();
        return QString::fromUtf8(ba, size);
    }