[issue33018] Improve issubclass() error checking and message

[Alexey Izbyshev]

Alexey Izbyshev <izbyshev at ispras.ru> added the comment:

PR 5944 changes ABC.__subclasscheck__ (not issubclass) to check its first argument, so if it's merged there will be no crash even with the revert.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33018>
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