adjustStackForRunStopStarting method Null safety

void adjustStackForRunStopStarting()

A RunStop keypress can resume a program, in which case the return stack should be left undisturbed. It can also start a "new" program run, so we need to be sure the return stack isn't in underflow

Implementation

void adjustStackForRunStopStarting() {
  if (returnStackUnderflow) {
    _returnStackPos = 0;
  }
}