(issue1788) Fix area split if there are no NaN's in the data The split algorithmn splits in a way that it always creates at least two datasets. One before the NaN, one after the NaN. This is broken in case the dataset does not contain any NaN value as it resulted in two identical datasets. This changed the display and resulted in a broken area calculation. I've also added some commented out debug code that was helpful tracking down this problem.

- Validation of the input values of an incoming feed() call