Fix integer underflow
Fix integer underflow

rust-lang/rustfmt,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,SingingTree/rustfmt,graydon/rust,aidancully/rust,Emilgardis/rustfmt,aidancully/rust,studoot/rustfmt,studoot/rustfmt,Emilgardis/rustfmt,rust-lang/rustfmt,aidancully/rust,graydon/rust,SingingTree/rustfmt,aidancully/rust,graydon/rust