fix hang on fstat calls in request server
fix hang on fstat calls in request server

Support fstat by converting to a standard Stat call and processing that.
I didn't want to add another special case to the request backend, I
wanted to keep it only having to support Stat.

fuchsia-mirror/third_party-pkg-sftp,pkg/sftp,ScriptRock/sftp,fuchsia-mirror/third_party-github.com-pkg-sftp