kitchen_pilot_wire_control.ino: switch off heater if we loose the wifi/MQTT

soft/kitchen/kitchen_pilot_wire_control/kitchen_pilot_wire_control.ino

@@ -54,4 +54,8 @@ void onConnectionEstablished()
 void loop()
 {
   client.loop();
+  if (!client.isConnected()) {
+    // if something wrong happens, switch off the heater
+    digitalWrite(heating_pin, HIGH);
+  }
 }