gh-107078: fix astimezone on Windows

[littlebutt]

• Fix _datetimemodule.c when calling datetime.datetime.fromtimestamp(0).astimezone() with OSError on Windows

• Issue: datetime.fromtimestamp(t).astimezone() fails for 0<=t<86400 in Windows #107078

[yabirgb]

Hello! Bumping the PR in case someone can take a look

[zooba]

I think we only want to do this if it's too small? Otherwise it has the potential to do the conversion wrong if you put in a "normal" time that's within max_fold_seconds of an offset change (either DST or legal change). We probably assume that none of these happened on the first day after epoch.

Otherwise, this seems like a fine way to handle it. A "real" fix would be much more complex, and probably inconsistent with actual timezone aware datetimes, which I'm sure are the preferred approach these days.

[serhiy-storchaka]

I agree with @zooba. See the Windows-specific comment in datetime_from_timet_and_us().

Also this change needs tests.

[serhiy-storchaka]

I agree with @zooba. See the Windows-specific comment in datetime_from_timet_and_us().

Also this change needs tests.

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[vstinner]

I merged #143463 instead. Thanks for your contribution anyway ;-)