message: Add an assertion to aid in tracking down a bug
diff: @@ -1038,9 +1038,11 @@ void Thread::PushPlan(ThreadPlanSP &thread_plan_sp) {
  if (thread_plan_sp) {
  // If the thread plan doesn't already have a tracer, give it its parent's
  // tracer:
  - if (!thread_plan_sp->GetThreadPlanTracer())
  + if (!thread_plan_sp->GetThreadPlanTracer()) {
  + assert(!m_plan_stack.empty());
  thread_plan_sp->SetThreadPlanTracer(
  m_plan_stack.back()->GetThreadPlanTracer());
  + }
  m_plan_stack.push_back(thread_plan_sp);
  thread_plan_sp->DidPush();
  