rust-openssl: MdCtxRef::digest_final() writes past caller buffer with no length check

rust-openssl provides OpenSSL bindings for the Rust programming language. From 0.10.39 to before 0.10.78, EVP_DigestFinal() always writes EVP_MD_CTX_size(ctx) to the out buffer. If out is smaller than that, MdCtxRef::digest_final() writes past its end, usually corrupting the stack. This is reachable from safe Rust. This vulnerability is fixed in 0.10.78.