cpp: Fix memory of DecryptionResult::symkeyAlgo
cpp: Fix memory of DecryptionResult::symkeyAlgo

* lang/cpp/src/decryptionresult.cpp (Private, ~Private): strdup
the symkey algo.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme