Fix for soft brush use on 256 colour sprite with no mask
Detail: Using a soft brush on a 256 colour sprite with no mask at all caused the screen to flash and wipes the whole sprite (seen in sprite file window, the sprite window itself not updated).
Detail: Using a soft brush on a 256 colour sprite with no mask at all caused the screen to flash and wipes the whole sprite (seen in sprite file window, the sprite window itself not updated).