Crash in `create_elementiter` when OOM

Crash report

What happened?

import _testcapi
from xml.etree.ElementTree import Element

e = Element('root')

_testcapi.set_nomemory(1, 2)
try:
    e.iter()
except MemoryError:
    pass
finally:
    _testcapi.remove_mem_hooks()

With UBSan enabled, I get:

Modules/_elementtree.c:2176:9: runtime error: applying non-zero offset 15914838024376868032 to null pointer
Segmentation fault         (core dumped)

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Output from running 'python -VV' on the command line:

No response

Linked PRs

• gh-148838
• gh-152120

从 Modules/_elementtree.c 中的 create_elementiter 附近开始，并在 UBSan 下使用 _testcapi.set_nomemory 重现报告的 e.iter() 情况。检查相关的 PR gh-148838 和 gh-152120；当内存不足路径不再触发空指针偏移诊断或段错误时，即表示完成。