U++

Buffer should also offer alternative method (Get) to ~operator that returns raw pointer.

The size could also be remembered and we should introduce Count() and IsEmpty() approach.
Something like:

dword length = ::GetShortPathName(static_cast<LPCTSTR>(path), nullptr, 0);
if(length == 0)
    return path;
Buffer<char> shortPathBuffer(length);

Could be easily refactor to:

Buffer<char> GetBufferForShortPath(const String& path)
{
    dword length = ::GetShortPathName(static_cast<LPCTSTR>(path), nullptr, 0);
    return Buffer<char> shortPathBuffer(length);
}

// The in the code:
Buffer<char> shortPathBuffer = GetBufferForShortPath(path);
if (shortPathBuffer.IsEmpty())
   return path;
else
    // Do something with the buffer...