gh-122081: fixed crash in decimal.IEEEContext() (#122082)

* gh-122081: fixed crash in decimal.IEEEContext()

Now

$ ./configure CFLAGS=-DEXTRA_FUNCTIONALITY -q && make -s && \
     ./python -m test test_decimal

- PASS

* Apply suggestions from code review

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

* Update Misc/NEWS.d/next/Library/2024-07-21-10-45-24.gh-issue-122081.dNrYMq.rst

* Apply suggestions from code review

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Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Kumar Aditya <kumaraditya@python.org>