FIX python client error not propagating

[anhqle]

Summary

Current code checks for the existence of response with if exc.response, which is a semantic bug because 400 responses are actually Falsy.

This PR removes this check (since exc.response should always exist anyway), ultimately allowing the error message to be propagated

Test Plan

• [ ] PR has an associated issue: #
• [x ] make check passes
• [x ] make test shows 100% unit test coverage

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[shangyian]

@anhqle just to check, you have permissions to merge PRs in this repo right?

[anhqle]

I think so, will let you know otherwise