Remove redundant check from tls1_get_curvelist

The function tls1_get_curvelist() has an explicit check to see if s->cert
is NULL or not. However the check appears *after* calling the tls1_suiteb
macro which derefs s->cert. In reality s->cert can never be NULL because
it is created in SSL_new(). If the malloc fails then the SSL_new call fails
and no SSL object is created.

Reviewed-by: Tim Hudson <tjh@openssl.org>