[mypyc] Fix crash on double yielding Iterators (#21826)

Closes https://github.com/mypyc/mypyc/issues/1210

This fixes another issue I ran into while trying to use `mypyc` for
`isort`.

I am aware the contributing guidelines say new contributors are not
encouraged to use LLMs but I hope this can get the same handling as
https://github.com/python/mypy/pull/21785. I have tried to ensure this
patch works as much as I can by:

Testing locally with `pytest mypyc/test/test_run.py `.
Tested that the test fails on `master` without the changes.
Also tried to run CI on my local fork
(https://github.com/DanielNoord/mypy/pull/2), which succeeded.

As with the previous PR, feel free to push changes to the branch or
cherry pick this into another branch. I just want to unblock `isort` :)