core: Ensure r_key init in gpgme_get_key
core: Ensure r_key init in gpgme_get_key

* src/keylist.c (gpgme_get_key): Move r_key init above
the first invalid value check.

--
This fixes the case where someone passes an unitialized
r_key and no fingerprint.

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