Setting attributes to None before saving can leave explainers broken if saving fails

[jklaise]

E.g.

alibi/alibi/saving.py

Line 111 in 91a2a88

explainer.predictor = None # type: ignore[attr-defined]

, if for some reason saving fails, the explainer is left without a predictor attribute and will not work anymore. We need to wrap saving in try/except and be careful to reset any changed attributes both on failure and success.