Сlose the old body explicitly after seek for S3. Fix #187

[inksink]

Solve issue #187

[mpenkov]

Why not be explicit and catch AttributeError?

[menshikh-iv]

I'm +1 too for catching more "restricted", after this fix I think we can merge.

[piskvorky]

Is it really only AttributeError? Cannot close() raise something else? (and if it does, should we care?)

[mpenkov]

@piskvorky I don't think we expect close itself to raise anything.

I think the intention here is to mimic the behavior of:

if body is not None:
    body.close()

without paying the price of the conditional every time. I think the author is assuming that most the time, the body will be non-null. I think this assumption is correct.

[inksink]

Right, if hasattr(self, '_body'), self._body must be io.BytesIO() or object.get()['Body'] (if it really raise something else, we should not care it and just raise it).
And I have changed Exception to AttributeError.