message: Add another check on controlStack.back()
diff: @@ -501,7 +501,10 @@ namespace IR
  ValueType popOperand()
  {
  - if(stack.size() > controlStack.back().outerStackSize)
  + if(controlStack.empty()) {
  + throw ValidationException("control stack empty");
  + }
  + else if(stack.size() > controlStack.back().outerStackSize)
  {
  const ValueType result = stack.back();
  stack.pop_back();
  