[476314] Deliver queued WS client msgs on reconnect.

Thanks to Joking Young and Christoph Krey.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=476314

ChangeLog.txt

@@ -1,6 +1,11 @@
 1.4.9 - 20160xxx
 ================
 
+Broker:
+- Ensure websockets clients that previously connected with clean session set
+  to false have their queued messages delivered immediately on reconnecting.
+  Closes #476314.
+
 Client library:
 - Fix the case where a message received just before the keepalive timer
   expired would cause the client to miss the keepalive timer.

src/websockets.c

@@ -218,6 +218,8 @@ static int callback_mqtt(struct libwebsocket_context *context,
 				return -1;
 			}
 
+			mqtt3_db_message_write(db, mosq);
+
 			if(mosq->out_packet && !mosq->current_out_packet){
 				mosq->current_out_packet = mosq->out_packet;
 				mosq->out_packet = mosq->out_packet->next;