The qx.util.Serializer.toJson fail on NaN integer

[nwgroup]

When av value have an NaN value, the JSOn structure fails.

To Reproduce Steps to reproduce the behavior:

1. Create an array with NaN value

[goldim]

@nwgroup Hello, could you describe the issue in more details please? What version of environment/qooxdoo/nodejs/etc do you use? Some code example also be wanted. What I've tried is:

const serer = qx.util.Serializer;
const res = serer.toJson([1, NaN]);
console.log(res);

qx v7.7.2 and there is no any errors. The output is fine.

[nwgroup]

Well, finally we found the problem on an RPC call with NaN values. For that reason our fix was: ` toJson(object, qxSerializer, dateFormat) {

  var result = "";
  // null or undefined
  if (object == null) {
    return "null";
  }

  if (Number.isNaN(object)) {
    return "null";
  }` 

and the RPC call got fine. We don't know if is better to commit that change or only apply for us. Thanks for the help!