fixed shift overflow
fixed shift overflow

Fix according to oli-obk
(https://github.com/rust-lang/rust/pull/58717#issuecomment-477494457)

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