Manually implement `is_zipfile` (#25279)
Summary:
The default implementation is lenient in that it recognizes a zipfile if the magic number appears anywhere in the archive. So if someone has the bytes `PK\x03\x04` in a tensor, it gets recognized as a zipfile. See https://bugs.python.org/issue28494
This implementation only checks the first 4 bytes of the file for the zip magic number. We could also copy https://github.com/python/cpython/pull/5053's fix, but that seems like overkill.
Fixes #25214
](https://our.intern.facebook.com/intern/diff/17102516/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25279
Pulled By: driazati
Differential Revision: D17102516
fbshipit-source-id: 4d09645bd97e9ff7136a2229fba1d9a1bce5665a
