Fix segfault in `THPGenerator_dealloc` (take 2) (#42510)
Summary:
Segfault happens when one tries to deallocate uninitialized generator.
Make `THPGenerator_dealloc` UBSAN-safe by moving implicit cast in the struct definition to reinterpret_cast
Add `TestTorch.test_invalid_generator_raises` that validates that Generator created on invalid device is handled correctly
Fixes https://github.com/pytorch/pytorch/issues/42281
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42510
Reviewed By: pbelevich
Differential Revision: D22917469
Pulled By: malfet
fbshipit-source-id: 5eaa68eef10d899ee3e210cb0e1e92f73be75712
