net: mqtt_sn: handle timestamp being 0

When running just the test mqtt_sn_client::test_mqtt_sn_wait_suback on
native_sim, the current timestamp is still 0. That caused the test to fail,
because 0 is used as an indicator, that the message has never been sent,
thus sending it every time process_work is executed.

Instead of adding additional variables and complexity, the code now simply
treats now==0 special and waits 1ms until doing anything.

Signed-off-by: Michael Zimmermann <[email protected]>

Author: M1cha

subsys/net/lib/mqtt_sn/mqtt_sn.c

@@ -664,7 +664,9 @@ static int process_pubs(struct mqtt_sn_client *client, int64_t *next_cycle)
 				"Processing publish for topic");
 		LOG_HEXDUMP_DBG(pub->pubdata, pub->datalen, "Processing publish data");
 
-		if (pub->con.last_attempt == 0) {
+		if (now == 0) {
+			next_attempt = 1;
+		} else if (pub->con.last_attempt == 0) {
 			next_attempt = 0;
 			dup = false;
 		} else {
@@ -749,7 +751,9 @@ static int process_topics(struct mqtt_sn_client *client, int64_t *next_cycle)
 	SYS_SLIST_FOR_EACH_CONTAINER(&client->topic, topic, next) {
 		LOG_HEXDUMP_DBG(topic->name, topic->namelen, "Processing topic");
 
-		if (topic->con.last_attempt == 0) {
+		if (now == 0) {
+			next_attempt = 1;
+		} else if (topic->con.last_attempt == 0) {
 			next_attempt = 0;
 			dup = false;
 		} else {