Indeed it looks like it is the source of the problem.

I created a patch to fix it.

But it looks like there is another problem, instead of crashing the
Python interpreter goes into interactive mode instead of executing the
'setup.py' script ...

I don't think it is related, I have checked the result of ws = ws +
wcslen(ws) and it seems to be correct.

I will investigate the problem and create another entry if it is unrelated.