message: Add error message in case reading from file fails while embedding
diff: @@ -1067,11 +1067,20 @@ struct EmbeddedSectionCommand : public Command
  bytebuf blob;
  fseek(f, 0, SEEK_END);
  - size_t len = (size_t)ftell(f);
  + int len = ftell(f);
  fseek(f, 0, SEEK_SET);
  - blob.resize(len);
  - fread(blob.data(), 1, len, f);
  + if(len < 0)
  + {
  + len = 0;
  + std::cerr << "I/O error reading from '" << file << "'" << std::endl;
  + }
  +
  + blob.resize((size_t)len);
  + size_t read = fread(blob.data(), 1, (size_t)len, f);
  +
  + if(read != (size_t)len)
  + std::cerr << "I/O error reading from '" << file << "'" << std::endl;
  fclose(f);
  