Fix some malloc failure crashes.

EVP_MD_CTX_copy_ex was implemented with a memcpy, which doesn't work well when
some of the pointers need to be copied, and ssl_verify_cert_chain didn't
account for set_ex_data failing.

Change-Id: Ieb556aeda6ab2e4c810f27012fefb1e65f860023
Reviewed-on: https://boringssl-review.googlesource.com/5911
Reviewed-by: Adam Langley <agl@google.com>
3 files changed