json: Fix crash on invalid json
json: Fix crash on invalid json

* src/gpgme-json.c (process_request): Init res. Check for
json object before encode and chunk.

--
If json is invalid we can't read chunksize and would crash
in encode and chunk.

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