Render histogram transfer function editor after histogram is set
Render histogram transfer function editor after histogram is set

The histogram transfer function chart was not updated after the
histogram was updated. One had to move the cursor over the histogram
transfer function chart to force a repaint.

This patch forces a repaint after the histogram data is set.

cjh1/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,cryos/tomviz,cjh1/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,thewtex/tomviz,mathturtle/tomviz,thewtex/tomviz,cryos/tomviz,OpenChemistry/tomviz,cjh1/tomviz,cryos/tomviz,thewtex/tomviz,OpenChemistry/tomviz