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

從 Modules/_elementtree.c 中的 create_elementiter 附近開始，並在 UBSan 下使用 _testcapi.set_nomemory 重現回報的 e.iter() 情況。檢視相關的 PR gh-148838 和 gh-152120；當記憶體不足路徑不再觸發 null 指標位移診斷或分段錯誤時，即表示完成。