RT3841: memset() cipher_data when allocated

If an EVP implementation (such as an engine) fails out early, it's
possible to call EVP_CIPHER_CTX_cleanup() which will call
ctx->cipher->cleanup() before the cipher_data has been initialized
via ctx->cipher->init().  Guarantee it's all-bytes-zero as soon as
it is allocated.

Reviewed-by: Matt Caswell <matt@openssl.org>

crypto/evp/evp_enc.c

@@ -165,6 +165,7 @@ int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,
                 EVPerr(EVP_F_EVP_CIPHERINIT_EX, ERR_R_MALLOC_FAILURE);
                 return 0;
             }
+            memset(ctx->cipher_data, 0, ctx->cipher->ctx_size);
         } else {
             ctx->cipher_data = NULL;
         }