Fix crash in dtls1_get_record whilst in the listen state where you get two

separate reads performed - one for the header and one for the body of the
handshake record.

CVE-2014-3571
Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/d1_pkt.c

@@ -645,8 +645,6 @@ again:
 		/* now s->packet_length == DTLS1_RT_HEADER_LENGTH */
 		i=rr->length;
 		n=ssl3_read_n(s,i,i,1);
-		if (n <= 0) return(n); /* error or non-blocking io */
-
 		/* this packet contained a partial record, dump it */
 		if ( n != i)
 			{

ssl/s3_pkt.c

@@ -197,6 +197,8 @@ int ssl3_read_n(SSL *s, int n, int max, int extend)
 	 * at once (as long as it fits into the buffer). */
 	if (SSL_IS_DTLS(s))
 		{
+		if (left == 0 && extend)
+			return 0;
 		if (left > 0 && n > left)
 			n = left;
 		}