Add Internal Server Error logging.

telegram-bot-api/Client.cpp

@@ -126,6 +126,7 @@ void Client::fail_query_with_error(PromisedQueryPtr query, int32 error_code, Sli
       break;
     case 500:
       prefix = Slice("Internal Server Error");
+      LOG(ERROR) << "Receive Internal Server Error: " << real_error_message;
       break;
     default:
       LOG(ERROR) << "Unsupported error " << real_error_code << ": " << real_error_message;