Starting a write transaction inside a write transaction will rollback the original transaction

[nirinchev]

The following awkward code fails in an even more awkward way:

final config = Configuration([Car.schema]);
final realm = Realm(config);
realm.write(() {
  // Second write inside the first one fails but the error is caught
  try {
    realm.write(() {});
  } catch (ex) {}
});

The error is:

RealmException: Could not commit write. Error code: 5 . Message: Can't commit a non-existing write transaction

What ends up happening is

1. We start the outer write
2. We start inner write
3. Inner write fails
4. We hit the realm.write catch block, which rolls back the outer transaction and rethrows
5. We catch the exception from the inner write
6. Realm tries to commit the outer write, which fails because the transaction was rolled back in 4.