Use `Iterator::all` instead of open-coding it
Use `Iterator::all` instead of open-coding it

Shorter code and by initializing to the final value directly, the variable
doesn't need to be mut.

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