core: Do not modify args for ignored failures
* src/op-support.c (_gpgme_parse_failure): Ignore gpg-exit failures before modifying args.
For op_decrypt_verify the status handler for both decrypt and
verify would parse the failure when the first parser ignored
the failure. This resulted in an ERR_INV_ENGINE as the first
call to parse_failure modified the args.
- GnuPG-Bug-Id: T3919