flatfs: not error out Walk in case of FileNotFound error

This is to prevent race that can happen while GCing the repo
Walk will build list of files and one of those files can be removed
by GC, currently it causes a failure which shouldn't be the case.

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>

flatfs/flatfs.go

@@ -313,6 +313,9 @@ func (fs *Datastore) Query(q query.Query) (query.Results, error) {
 	go func() {
 		defer close(reschan)
 		err := filepath.Walk(fs.path, func(path string, info os.FileInfo, err error) error {
+			if os.IsNotExist(err) {
+				return nil
+			}
 			if err != nil {
 				log.Errorf("Walk func in Query got error: %v", err)
 				return err