fix sumbuffer to initialize its top and left colum/row with zeros. Without this fix we were effectively chopping off the top row of pixels when we computed a blur.
fix sumbuffer to initialize its top and left colum/row with zeros. Without this fix we were
effectively chopping off the top row of pixels when we computed a blur.



csulmone/skia,csulmone/skia,csulmone/skia,csulmone/skia