Fix the error handling in CRYPTO_dup_ex_data.

Fix a strict aliasing issue in ui_dup_method_data.
Add test coverage for CRYPTO_dup_ex_data, use OPENSSL_assert.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2988)