Fix PDF417 with binary content not producing any output with ZXing 2.0

There's two issues here:
- The QByteArray to std::wstring conversion has to use unsigned bytes, the
previous code did an implicit conversion to int producing wrong results for
value above 127.
- We now have to explicitly specify we are inputting binary data.

See also https://github.com/zxing-cpp/zxing-cpp/pull/557.

This fixes for example domestic Hungarian railway ticket barcodes not
being shown in KDE Itinerary anymore.

(cherry picked from commit 6b234bc7)