Fix CalculateActualInterval() stuck in infinite loop (#758).
Fix CalculateActualInterval() stuck in infinite loop (#758).

objorke/oxyplot,GeertvanHorrik/oxyplot,olegtarasov/oxyplot,objorke/oxyplot,objorke/oxyplot,shoelzer/oxyplot,GeertvanHorrik/oxyplot,shoelzer/oxyplot,Jofta/oxyplot,DotNetDoctor/oxyplot,olegtarasov/oxyplot,HermanEldering/oxyplot,oxyplot/oxyplot,Kaplas80/oxyplot,shoelzer/oxyplot,Kaplas80/oxyplot,Isolocis/oxyplot,zur003/oxyplot,ze-pequeno/oxyplot,Jonarw/oxyplot,GeertvanHorrik/oxyplot,DotNetDoctor/oxyplot,NilesDavis/oxyplot,HermanEldering/oxyplot