[WPF] Fixed "drag image must be set before starting drag operation" exception in "TreeViews" sample
[WPF] Fixed "drag image must be set before starting drag operation" exception in "TreeViews" sample

lytico/xwt,TheBrainTech/xwt,mono/xwt,hamekoz/xwt,antmicro/xwt,hwthomas/xwt,cra0zy/xwt