Fix restic for i386

Some functions aren't implemented on Linux/i386, e.g. user.LookupId()
and user.Current(), so ignore these errors.

node.go

@@ -389,16 +389,18 @@ func lookupUsername(uid string) (string, error) {
 		return value, nil
 	}
 
+	username := ""
+
 	u, err := user.LookupId(uid)
-	if err != nil {
-		return "", err
+	if err == nil {
+		username = u.Username
 	}
 
 	uidLookupCacheMutex.Lock()
-	uidLookupCache[uid] = u.Username
+	uidLookupCache[uid] = username
 	uidLookupCacheMutex.Unlock()
 
-	return u.Username, nil
+	return username, nil
 }
 
 func (node *Node) fillExtra(path string, fi os.FileInfo) error {

snapshot.go

@@ -71,10 +71,10 @@ func (sn Snapshot) ID() backend.ID {
 func (sn *Snapshot) fillUserInfo() error {
 	usr, err := user.Current()
 	if err != nil {
-		return err
+		return nil
 	}
-
 	sn.Username = usr.Username
+
 	uid, err := strconv.ParseInt(usr.Uid, 10, 32)
 	if err != nil {
 		return err