Negative date do not display correctly in the widget and are considered invalid in the result

[Voldenuix]

After updating Sparnatural on the 11.0 version in OpenArcheao, the display of a negative date in the date widget seems broken.
It'd automatically change the negative date to a positive one :

While in the SPARQL query everything seems fine :

The negative dates will also be showned as « Invalid Date » in the result :

After some research, the problem might comes from the way ValueLabel is handled in DateWidget.ts :

    let lbl = "";

    if (start != "" && start) {
      lbl = lbl.concat(` ${start.toISOString().slice(0, 10)}`);
    }
    if (stop && stop != "") {
      lbl = lbl.concat(` - ${stop.toISOString().slice(0, 10)}`);
    }
    return lbl;
  };

The .toISOSting() function convert the String to a Javascript Date format, which doesn't support negative dates (hence the Invalid Date result).
It might be interesting to add a check if the start or stop date is negative, in order to keep it as a string and not use the toISOString() function.