message: Call png_error if reading fails
  Allows faster exit from reading corrupt PNG files.
diff: @@ -90,11 +90,8 @@ void WarningHandler(png_structp png_ptr, png_const_charp msg) {
  void StringReader(png_structp png_ptr, png_bytep data, png_size_t length) {
  DecodeContext* const ctx = bit_cast<DecodeContext*>(png_get_io_ptr(png_ptr));
  if (static_cast<png_size_t>(ctx->data_left) < length) {
  - if (!ctx->error_condition) {
  - VLOG(1) << "PNG read decoding error";
  - ctx->error_condition = true;
  - }
  memset(data, 0, length);
  + png_error(png_ptr, "More bytes requested to read than available");
  } else {
  memcpy(data, ctx->data, length);
  ctx->data += length;
  