message: [PE] prevent integer underflow when padding sections
diff: @@ -540,15 +540,18 @@ Builder& Builder::operator<<(const Section& section) {
  std::copy(name, name + sizeof(header.Name), std::begin(header.Name));
  this->ios_.write(reinterpret_cast<uint8_t*>(&header), sizeof(pe_section));
  -
  + size_t pad_length = 0;
  if (section.content().size() > section.size()) {
  LOG(WARNING) << section.name()
  << " content size is bigger than section's header size"
  << std::endl;
  }
  + else {
  + pad_length = section.size() - section.content().size();
  + }
  // Pad section content with zeroes
  - std::vector<uint8_t> zero_pad (section.size() - section.content().size(), 0);
  + std::vector<uint8_t> zero_pad (pad_length, 0);
  const size_t saved_offset = this->ios_.tellp();
  this->ios_.seekp(section.offset());
  