TT#14008 fix MQTT global stats

The JSON context is already in an object, therefore skip the surrounding
{} enclosure.

Also don't run the global MQTT timer when MQTT is disabled.

closes #1290

Change-Id: I63c622bd339545e625ee18def33f21de2533f949

daemon/call.c

@@ -725,7 +725,8 @@ int call_init() {
 
 	poller_add_timer(rtpe_poller, call_timer, NULL);
 
-	mqtt_timer_start(&global_mqtt_timer, NULL, NULL);
+	if (mqtt_publish_scope() != MPS_NONE)
+		mqtt_timer_start(&global_mqtt_timer, NULL, NULL);
 
 	return 0;
 }

daemon/mqtt.c

@@ -388,6 +388,12 @@ static void mqtt_global_stats(JsonBuilder *json) {
 		if (!m->label)
 			continue;
 
+		if (m->is_bracket && l == metrics->head) // skip initial {
+			continue;
+		if (m->is_bracket && l == metrics->tail) // skip final }
+			continue;
+
+
 		if (m->value_short) {
 			json_builder_set_member_name(json, m->label);
 			if (m->is_int)