Fix - Stacked Bar throwing console errors when columns have varied n of stacks (#640)
Fix - Stacked Bar throwing console errors when columns have varied n of stacks (#640)

* Fix - Stacked Bar throwing console errors when columns have differnet number of stacks

* Reset demo

* Create private function that filters out unknown values

martinmanzo/britecharts,martinmanzo/britecharts,martinmanzo/britecharts