fdo#43681: Set correct auto scaling for stacked data series.
fdo#43681: Set correct auto scaling for stacked data series.

With this change, the automatic y-axis scaling should be more accurate
for stacked charts (i.e. stacked line, area, bar charts) with dates on
the x-axis.  The previous algorithm only calculated the max and min
y-values of the individual data, without taking into account the stacking
type when the x-axis type was date.

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core