Merge branch 'cb/open-noatime-clear-errno' into maint

When trying to see that an object does not exist, a state errno leaked from our "first try to open a packfile with O_NOATIME and then if it fails retry without it" logic on a system that refuses O_NOATIME. This confused us and caused us to die, saying that the packfile is unreadable, when we should have just reported that the object does not exist in that packfile to the caller. * cb/open-noatime-clear-errno: git_open_noatime: return with errno=0 on success