look up descriptor by objclass in _getattr instead of eval

[alhudz]

_getattr reconstructs slot/getset/method descriptors on unpickle.

Repro: _getattr(object, '__doc__"].count("zz") or setattr(__import__("dill"),"_pwned",True) or object.__dict__["__doc__', "x'x'x'object'x") runs the injected setattr; a crafted pickle reducing to _getattr reaches the same eval on load.
Cause: the fast path eval(attr+'.__dict__["'+name+'"]') evaluates a string built from the pickled repr_str/name; the except branch already returns the identical descriptor via objclass.__dict__[name].
Fix: drop the eval branch and always resolve through objclass. repr_str is now unused but kept in the signature so existing pickles still load.