Python run_method API segfaults if given non-existent method

[swolchok]

🐛 Describe the bug

Repro:

1. install executorch with ./install_requirements.sh --pybind

>>> from executorch.extension.pybindings import portable_lib as exec_lib
>>> mod = exec_lib._load_for_executorch("some.pte")
>>> mod.run_method("idontexist")
fish: Job 1, 'python' terminated by signal SIGSEGV (Address boundary error)

Versions

latest executorch main, commit hash cd46721

[Olivia-liu]

@JacobSzwejbka @dbort Iiuc, this is an ask for better error handling when the user tries to run a method that doesn't exist.

[dbort]

We should definitely throw a python exception instead of segfaulting.

[JacobSzwejbka]

Looking

[JacobSzwejbka]

https://github.com/pytorch/executorch/blob/main/extension/pybindings/pybindings.cpp#L252 lol