agent: For OCB key files return Bad Passprase instead of Checksum Error.
* agent/protect.c (do_decryption): Map error checksum to bad passpharse protection * agent/call-pinentry.c (unlock_pinentry): Don't munge the error source for corrupted protection.
- GnuPG-bug-id: T3266
- Signed-off-by: Werner Koch <wk@gnupg.org>