Split from T7341
Decryption of corrupted OpenPGP encrypted messages result in feedback "Keine Daten" (no data), which is misleading.
To reproduce:
- Open Notepad
- Enter some text
- Select some valid OpenPGP Sign/Encrypt Certs
- Click Sign / Encrypt Notepad Button
- Change one char of the encrypted text
- Click Decrypt / Verify Notepad
- Compare Keine Daten with result feedback in Diagnostics
Some diagnostic results depending on which char was edited:
| "keine gültigen OpenPGP-Daten" (better than just "no data") |  |
| "Prüfsummenfehler" |  |
| "Falsch aufgebaute Prüfsumme" |  |
| "unknown version" |  |
I'd prefer "Keine gültigen (OpenPGP-)Daten" for the first case (probably someone missed a dash to copy).
I'm not sure, if the technical reason should be displayed for the other cases, but at least it should be clear, that it's due to some technical reason (corrupted message, copy&paste error, etc).
Note: SMIME feedback is better, the technical reason is mostly displayed.