Remove const from outbuf

[BradleyMarie]

The const marking on outbuf/buffer means that the buffer allocated by SaveEXRToMemory cannot be passed to free without a compiler error.

For example, the following code will not compile because SaveEXRToMemory requires buffer to be const.

bool Write(const std::vector<float>& image, std::pair<int, int> size,
           std::ostream& output) {
  const unsigned char* buffer;  // Required to be const by signature of SaveEXRToMemory
  int bytes_written =
      SaveEXRToMemory(image.data(), /*width=*/size.second,
                      /*height=*/size.first, /*components=*/3,
                      /*save_as_fp16=*/1, /*buffer=*/&buffer, /*err=*/nullptr);

  if (bytes_written < 0) {
    return false;
  }

  output.write(reinterpret_cast<const char*>(buffer),
               static_cast<std::streamsize>(bytes_written));

  free(buffer);  // This line triggers a compile error

  return true;
}

Unfortunately, this is a breaking API change but since it wasn't possible to call free on the allocated buffer without either a compiler error or a const-cast, I believe this break is a necessary evil.

[syoyo]

Good find! Thanks!

breaking API change

This should be OK. There was no use of SaveEXRToMemory in TinyEXR examples/tests so couldn't find the const issue. Probably no one got success to use SaveEXRToMemory...