[Functorch] Make minpybind less likely to crash (#84788)
Error handling in `vector_args::parse` is fundamentally broken, as it
calls to
[`_PyArg_ParseStackAndKeywords`](https://github.com/python/cpython/blob/000593c0f97ac9b75b56064a957b84a3aaa60674/Include/modsupport.h#L106)
variadic function, which are
akin to `sscanf` without any arguments, which results, in case of partial
parse in a random segfault/stack corruption. Remedy it by passing a few
references to dummy pyobject
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84788
Approved by: https://github.com/zou3519
