Assertion on late error variable in NNBD version of Future.wait is too early

[leafpetersen]

The following program causes a late initialization error when run with the NNBD SDK and asserts enabled:

import 'dart:async';

Future test() async {
  try {
    var f1 = Future(() => throw "Error");
    var f2 = Future(() => 3);
    await Future.wait([f1, f2], eagerError : true);
  } catch (_) {
    return -1;
  }
  return 0;
}

void main() async {
  var f = test();
  await f;
}

The assert on line 415 that was added is too early. In the case that eagerError is true and an earlier future has thrown an error, values may have been set to null but error has not yet been set.

[leafpetersen]

https://dart-review.googlesource.com/c/sdk/+/144809