message: Fix out of bounds access if some threads have exited
diff: @@ -1794,7 +1794,8 @@ void Debugger::CalcActiveMask(rdcarray<bool> &activeMask)
  rdcarray<bool> inConverge;
  inConverge.resize(activeMask.size());
  for(size_t i = 0; i < workgroup.size(); i++)
  - inConverge[i] = (workgroup[i].callstack.back()->curBlock == convergeBlock);
  + inConverge[i] = (!workgroup[i].callstack.empty() &&
  + workgroup[i].callstack.back()->curBlock == convergeBlock);
  // is any thread active, but not converged?
  bool anyActiveNotConverged = false;
  