Only reset the ctx when a cipher is given

This restores the 1.0.2 behaviour

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Benjamin Kaduk <bkaduk@akamai.com>
GH: #4613

crypto/evp/evp_enc.c

diff --git a/crypto/evp/evp_enc.c b/crypto/evp/evp_enc.c
index d353084..f89cff6 100644
--- a/crypto/evp/evp_enc.c
+++ b/crypto/evp/evp_enc.c
@@ -50,7 +50,8 @@
 int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,
                    const unsigned char *key, const unsigned char *iv, int enc)
 {
-    EVP_CIPHER_CTX_reset(ctx);
+    if (cipher != NULL)
+        EVP_CIPHER_CTX_reset(ctx);
     return EVP_CipherInit_ex(ctx, cipher, NULL, key, iv, enc);
 }