Handle unparsable but valid response

[Ephigenia]

In some cases (at least one, indicated in #26) the IKEA iows API replies with a different JSON format than expected. In that case an exception is thrown while there are other stores valid. There should be a special soft-handling of unparsable json response formats which results in a similar output like a 404 (cli-stock.js:122) so that it’s possible to find out which store raises the error.