Adjust the zero check in `RawVec::grow`.
Adjust the zero check in `RawVec::grow`.

This was supposed to land as part of #72227. (I wish `git push` would
abort when you have uncommited changes.)

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust