Ignore users' configuration diff.noprefix

[SheffeyG]

Recently when I trying to discard a hunk with neogit, an error raised: hunk has no filepath, It turns out somehow I set the diff.norefix in my global git configurations, while neogit rely on the prefix a/ and b/ for location. so we should alway set diff.nopreix to false when building command.

[CKolkey]

Thanks! Didn't know that one