Add checks to the return value of EVP_Cipher to prevent silent encryption failure.

PR#1767

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit 244d0955ad)

ssl/d1_enc.c

@@ -241,7 +241,8 @@ int dtls1_enc(SSL *s, int send)
 				return 0;
 			}
 		
-		EVP_Cipher(ds,rec->data,rec->input,l);
+		if(EVP_Cipher(ds,rec->data,rec->input,l) < 1)
+			return -1;
 
 #ifdef KSSL_DEBUG
 		{