message: Fix a thinko in getting the persistent_expression_state.
  For swift it was getting the value but then not setting it
  to anything.
diff: @@ -106,6 +106,7 @@ ValueObjectSP ABI::GetReturnValueObject(Thread &thread, CompilerType &ast_type,
  PersistentExpressionState *persistent_expression_state;
  auto target = thread.CalculateTarget();
  if (lang == lldb::eLanguageTypeSwift)
  + persistent_expression_state =
  target->GetSwiftPersistentExpressionState(thread);
  else
  persistent_expression_state =
  