Add output process error handling
This adds error handling for the output process similar to:
0ebc73bb2248af0b6affefe0083287354dbd92a4
Previously output process errors were ignored and the decryption
was shown as successful even if a corrupted tar archive was
extracted. This lead to mysterious missing files after
the decryption of corrupted archives.
- GnuPG-Bug-Id: T4332