addAll() is folded wrongly when index is used

[sabi0]

In this particular case (when index = 0) the best folding is probably this: vCharSequence = sequence + vCharSequence;

In case the index is different from 0 I don't think it can be folded without loosing semantics. Unless you are willing to bother with slices like: vCharSequence = vCharSequence[:3] + sequence + vCharSequence[3:]