Optimize FromIterator<OsString> to reuse the first allocation
Optimize FromIterator<OsString> to reuse the first allocation

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