Fix lifetime confusion in shadow stack pass

[dcodeIO]

Potential fix for the errors observed in #2594, and prior in #2575.

let outer = null;
while (condition) {
  let inner = value;
  outer = inner; // here
}

Previously, at // here, no shadow stack slot was populated, assuming that inner respectively value is already kept alive by another slot. In a loop, this assumption doesn't hold obviously, since if inner is reassigned a different value in a subsequent iteration, the previous value copied to outer is, due to skipping the stack slot, no longer kept alive.

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[CountBleck]

Looks good to me. It would be nice if slots could still be omitted by checking lifetimes somehow.