Fix a memory leak in tls1_mac

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5650)

ssl/record/ssl3_record.c

diff --git a/ssl/record/ssl3_record.c b/ssl/record/ssl3_record.c
index 4ffc842..fa902f3 100644
--- a/ssl/record/ssl3_record.c
+++ b/ssl/record/ssl3_record.c
@@ -1297,8 +1297,10 @@
         mac_ctx = hash;
     } else {
         hmac = EVP_MD_CTX_new();
-        if (hmac == NULL || !EVP_MD_CTX_copy(hmac, hash))
+        if (hmac == NULL || !EVP_MD_CTX_copy(hmac, hash)) {
+            EVP_MD_CTX_free(hmac);
             return 0;
+        }
         mac_ctx = hmac;
     }