GetEnvironmentVariable(), mismatched delete / delete[] on windows

[marcalff]

Found by @owent.

In the main branch, in the following code:

// Returns the env variable set.
inline const std::string GetEnvironmentVariable(const char *env_var_name)
{
#if !defined(NO_GETENV)
  const char *endpoint_from_env = nullptr;
#  if defined(_MSC_VER)
  // avoid calling std::getenv which is deprecated in MSVC.
  size_t required_size = 0;
  getenv_s(&required_size, nullptr, 0, env_var_name);
  std::unique_ptr<char> endpoint_buffer;
  if (required_size > 0)
  {
    endpoint_buffer = std::unique_ptr<char>{new char[required_size]};
    getenv_s(&required_size, endpoint_buffer.get(), required_size, env_var_name);
    endpoint_from_env = endpoint_buffer.get();
  }
#  else
  endpoint_from_env = std::getenv(env_var_name);
#  endif  // defined(_MSC_VER)
  return endpoint_from_env == nullptr ? std::string{} : std::string{endpoint_from_env};
#else
  return std::string{};
#endif  // !defined(NO_GETENV)
}

This part:

  std::unique_ptr<char> endpoint_buffer;
  endpoint_buffer = std::unique_ptr<char>{new char[required_size]};

will cause an invalid call to delete when releasing the unique pointer.

The data is an array, so the code should be:

  std::unique_ptr<char[]> endpoint_buffer;
  endpoint_buffer = std::unique_ptr<char[]>{new char[required_size]};

Verified on linux, by putting the same code outside of ifdef _MSC_VER, and tested with valgrind.

==12501== Mismatched free() / delete / delete []
==12501==    at 0x4C3768B: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==12501==    by 0x833AFA: std::default_delete<char>::operator()(char*) const (unique_ptr.h:95)
==12501==    by 0x83382C: std::unique_ptr<char, std::default_delete<char> >::~unique_ptr() (unique_ptr.h:396)