Harmonize return values in dtls1_buffer_record

Ensure all malloc failures return -1.

Reported by Adam Langley (Google).
Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/d1_pkt.c

@@ -231,7 +231,7 @@ dtls1_buffer_record(SSL *s, record_pqueue *queue, unsigned char *priority)
             pitem_free(item);
 
         SSLerr(SSL_F_DTLS1_BUFFER_RECORD, ERR_R_INTERNAL_ERROR);
-        return (0);
+        return -1;
     }
 
     rdata->packet = s->packet;