cipher: Clear AESWRAP scratch area immediately after use
* cipher/cipher-aeswrap.c (_gcry_cipher_aeswrap_decrypt): Call wipememory.
Note that gcry_cipher_close will do this also but some applications
keep the context for a long time and thus plaintext could be found in
memory during the time the context is open.
- GnuPG-bug-id: T5597