show MQTT connection error only once on the first connect failure

src/core/mqtt.cpp

@@ -472,8 +472,8 @@ bool Mqtt::get_publish_onchange(uint8_t device_type) {
     return false;
 }
 void Mqtt::on_disconnect(espMqttClientTypes::DisconnectReason reason) {
-    // only show the error once, not every 2 seconds
-    if (!connecting_) {
+    // only show the error once on the first connect failure
+    if (connectcount_) {
         return;
     }
     connecting_ = false;