Rollup merge of #35182 - frewsxcv:nulerror, r=steveklabnik
Rollup merge of #35182 - frewsxcv:nulerror, r=steveklabnik

Add doc example for `std::ffi::NulError::nul_position`.

None

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