Improve bug! message for impossible case in Relate
Improve bug! message for impossible case in Relate

Hitting this branch in Clippy and I think it makes sense to print
both values here in case other people hit this branch, too.

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