Undefined behavior with memset of std::string to 0 (#18703)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18703
`zeroPtr` is sometimes a `std::string` tensor, so `memset` to 0 is undefined behavior.
This might be accidentally safe with `std::string` implementation that use SSO (Small String Optimization), but will crash otherwise.
Reviewed By: zheng-xq
Differential Revision: D14714458
fbshipit-source-id: 012a18464e6514d38ff791509b88ddc3fc55b2b1
