Fixed printForDebug : don't call stoi on empty cell

reading_machine/src/Config.cpp

@@ -146,7 +146,7 @@ void Config::printForDebug(FILE * dest) const
       std::string toPrintCol = colContent;
       try
       {
-        if (getColName(i) == headColName && toPrintCol != "_")
+        if (getColName(i) == headColName && toPrintCol != "_" && !toPrintCol.empty())
           if (toPrintCol != "0")
             toPrintCol = getAsFeature(idColName, std::stoi(toPrintCol));
       } catch(std::exception & e) {util::myThrow(fmt::format("toPrintCol='{}' {}", toPrintCol, e.what()));}