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

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