json: Delete primary key if subkey gen fails
json: Delete primary key if subkey gen fails

* src/gpgme-json.c (op_delete): Delete primary key on
subkey gen error.

--
This can happen for example if the user cancels the
pinentry to unlock the primary key when adding the
subkey.  To avoid an artifact of a pimary key without
an encryption capable subkey we delete the created
key and treat the whole operation as failed.

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