def set_pixel_if_within_bounds(x, y, color)
      return unless include_xy?(x, y)
      @pixels[y * width + x] = color
    end
def set_pixel_if_within_bounds(x, y, color)
      return unless include_xy?(x, y)
      @pixels[y * width + x] = color
    end
Replaces a single pixel in this canvas, with bounds checking. It will do
 noting if the provided coordinates are out of bounds.

 @param [Integer] x The x-coordinate of the pixel (column)
 @param [Integer] y The y-coordinate of the pixel (row)
 @param [Integer] color The new color value for the provided coordinates.
 @return [Integer] The new color value for this pixel, i.e.
   <tt>color</tt>, or <tt>nil</tt> if the coordinates are out of bounds.