nss: Don't leak memory on parse error

nss: Don't leak memory on parse error

If yajl_parse() fails, we try to print an error message. For
that, yajl_get_error() is used. However, its documentation say
that caller is also responsible for freeing the memory it
allocates by using yajl_free_error().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>