Fix calculation of remaining length parameter for websockets clients.

Only affects those clients that send fragmented packets.

Closes #1974. Thanks to 贺亚东.

ChangeLog.txt

@@ -1,3 +1,11 @@
+2.0.6 - 2021-01-xx
+==================
+
+Broker:
+- Fix calculation of remaining length parameter for websockets clients that
+  send fragmented packets. Closes #1974.
+
+
 2.0.5 - 2021-01-11
 ==================
 

src/websockets.c

@@ -332,7 +332,7 @@ static int callback_mqtt(
 						mosq->in_packet.remaining_length += (byte & 127) * mosq->in_packet.remaining_mult;
 						mosq->in_packet.remaining_mult *= 128;
 					}while((byte & 128) != 0);
-					mosq->in_packet.remaining_count = (int8_t)(mosq->in_packet.remaining_count -1);
+					mosq->in_packet.remaining_count = (int8_t)(mosq->in_packet.remaining_count * -1);
 
 					if(mosq->in_packet.remaining_length > 0){
 						mosq->in_packet.payload = mosquitto__malloc(mosq->in_packet.remaining_length*sizeof(uint8_t));