third_party/libpng: update to 1.2.54

TBR=darin@chromium.org
BUG=560291

Review URL: https://codereview.chromium.org/1467263003

Cr-Commit-Position: refs/heads/master@{#362298}
png_get_image_width(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr != NULL && info_ptr != NULL)
      return info_ptr->width;

   return (0);
}

png_get_image_width(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr != NULL && info_ptr != NULL)
      return info_ptr->width;

   return (0);
}
