ssl/t1_enc.c: check EVP_MD_CTX_copy return value.

PR: 3201

ssl/t1_enc.c

diff --git a/ssl/t1_enc.c b/ssl/t1_enc.c
index 28471c2..a98f6fe 100644
--- a/ssl/t1_enc.c
+++ b/ssl/t1_enc.c
@@ -1009,7 +1009,8 @@
 		}
 		else
 		{
-			EVP_MD_CTX_copy(&hmac,hash);
+			if (!EVP_MD_CTX_copy(&hmac,hash))
+				return -1;
 			mac_ctx = &hmac;
 		}