[Mac] Fix NRE in CanvasCellView
[Mac] Fix NRE in CanvasCellView

CanvasCellView expects the backend to implement
ICanvasCellViewBackend.QueueDraw.

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