formatfloat wrong return in unicode_format.c

[aisk]

Bug report

Bug description:

Original gist: https://gist.github.com/devdanzin/577421b083bad6802aa391b909d1a725

formatfloat (line 163): Returns 0 (success) when _PyUnicode_FromASCII fails. Caller has safety net, but violates return-value contract.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-151845: Fix formatfloat() return-value contract in unicode_format.c #151846
• [3.15] gh-151845: Fix formatfloat() return-value contract in unicode_format.c (GH-151846) #151865