Allow reloadData if previous animation ongoing.
Allow reloadData if previous animation ongoing.

Before this a slice could be missed if it was added during a previous animation.

pmaccamp/XYPieChart,natecope/XYPieChart,mattayasu/XYPieChart,DSandfeld/XYPieChart,zuojx1013/XYPieChart,edwinfinch/XYPieChart,UB12/X_Y,lukaszmargielewski/XYPieChart,danydev/XYPieChart,damoncoo/XYPieChart,Jaelene/XYPieChart,Farteen/XYPieChart,xyfeng/XYPieChart,rollokb/XYPieChart