Do not reset bind address option if passed NULL.

mosquitto_connect_bind_async() and mosquitto_connect_bind_v5() should not
reset the bind address option if called with bind_address == NULL.

Otherwise calling mosquitto_connect_async() will *force* the bind
address to be reset, even if previously set with
mosquitto_string_option().

ChangeLog.txt

@@ -1,6 +1,8 @@
 Broker:
 - Fix $SYS/broker/publish/messages/+ counters not being updated for QoS 1, 2
   messages. Closes #1968.
+- mosquitto_connect_bind_async() and mosquitto_connect_bind_v5() should not
+  reset the bind address option if called with bind_address == NULL.
 
 
 2.0.3 - 2020-12-17

lib/connect.c

@@ -96,8 +96,10 @@ int mosquitto_connect_bind_v5(struct mosquitto *mosq, const char *host, int port
 {
 	int rc;
 
+	if(bind_address){
 		rc = mosquitto_string_option(mosq, MOSQ_OPT_BIND_ADDRESS, bind_address);
 		if(rc) return rc;
+	}
 
 	mosquitto_property_free_all(&mosq->connect_properties);
 	if(properties){
@@ -128,8 +130,10 @@ int mosquitto_connect_bind_async(struct mosquitto *mosq, const char *host, int p
 {
 	int rc;
 
+	if(bind_address){
 		rc = mosquitto_string_option(mosq, MOSQ_OPT_BIND_ADDRESS, bind_address);
 		if(rc) return rc;
+	}
 
 	rc = mosquitto__connect_init(mosq, host, port, keepalive);
 	if(rc) return rc;