Fix axis orientation was swapped when the diagram was vertical.

This can be verified by loading the ODP referenced at bug 287895
into Stage. There at slide number 9 we displayed only one big
bar rather then all the bars with the expected at the y-axis
defined chart:maximum. That was so cause we completly ignored
any vertical=true definitions for the axes cause Axis::loadOdf
was called way before we called PlotArea::setVertical.