Apparently this can actually make a difference in some cases, and the
C++ Core Guideliens recommend doing this on all default constructors,
destructors, and all functions that can not throw (and thus also don't
allocate).
`std::char_traits<wchar_t>::length()` would return the wrong length for
a wide string under Wine, and thus also for `String128`. This would
cause parts of the strings to get cut off. As a workaround we'll just
serialize the entire container including all null bytes at the end.