Fix the crash due to inconsistent enc_write_ctx

- add error handling in ssl3_generate_key_block and ssl3_change_cipher_state

Fixes #2114

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2137)