If client doesn't send curves list, don't assume all.
If client doesn't send curves list, don't assume all.

Reviewed-by: Viktor Dukhovni <86faeb3e05561b856666236e198c27e698275e82@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1597)
openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl