message: [expression parser] Allow 0-sized structs during dematerialization.
  We have special handling for them during materialization; this is the
  same special case going the other way.
  <rdar://problem/33666307>
diff: @@ -674,6 +674,12 @@ public:
  extract_error);
  if (!extract_error.Success()) {
  + if (valobj_type.GetMinimumLanguage() == lldb::eLanguageTypeSwift &&
  + valobj_type.GetByteSize(frame_sp.get()) == 0) {
  + // We don't need to dematerialize empty structs in Swift.
  + return;
  + }
  +
  err.SetErrorStringWithFormat("couldn't get the data for variable %s",
  m_variable_sp->GetName().AsCString());
  return;
  