fix small typo in MQTT override code

bracket was on wrong position, resulting in this warning:

wled00/set.cpp:357:79: warning: value computed is not used [-Wunused-value]
     strlcpy(mqttGroupTopic, request->arg(F("MG")).c_str(), MQTT_MAX_TOPIC_LEN)+1;

wled00/set.cpp

@@ -354,7 +354,7 @@ void handleSettingsSet(AsyncWebServerRequest *request, byte subPage)
     if (!isAsterisksOnly(request->arg(F("MQPASS")).c_str(), 41)) strlcpy(mqttPass, request->arg(F("MQPASS")).c_str(), 65);
     strlcpy(mqttClientID, request->arg(F("MQCID")).c_str(), 41);
     strlcpy(mqttDeviceTopic, request->arg(F("MD")).c_str(), MQTT_MAX_TOPIC_LEN+1);
-    strlcpy(mqttGroupTopic, request->arg(F("MG")).c_str(), MQTT_MAX_TOPIC_LEN)+1;
+    strlcpy(mqttGroupTopic, request->arg(F("MG")).c_str(), MQTT_MAX_TOPIC_LEN+1);
     buttonPublishMqtt = request->hasArg(F("BM"));
     retainMqttMsg = request->hasArg(F("RT"));
     #endif