Multiple normalized series causes "seriesData.forEach not defined"-Exception

Because seriesData is null at this point. The data does contain less elements than this.series. 
btw: Iterating over an array with the index of another array seems dangerous to me. So my quick fix won't be the best one anyway.

Example code can be found here: https://github.com/unSinn/plant-vertx/blob/master/webroot/js/plant.js
Merge pull request #258 from unSinn/patch-1

Multiple normalized series causes "seriesData.forEach not defined"-Excep...