In 3d2ca8104e some change were introduced to the graph view.
But part of it had no sense when displaying data over 2 group by.
eg. if the first level has 2 groups (2018, 2019) and each second level 2
groups (Done,Cancelled), we could have:
2018/Done: 0
2018/Cancelled: 5
2019/Done: 8
2019/Cancelled: 9
this gives us two main groups [2018: 5] / [2019: 17], the code
remove the 2018 because [2018/Done] is 0 so we have something odd
with columns not in order, and in stacked bar chart some part of
a bar at the wrong offset
opw-1932517
closes#30529
Nicolas Lempereur
ce6e66cef9