Return and log errors in Walk function

We have some random crashes there and it would be good
to know what are erros that are causing those crashes.

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

flatfs/flatfs.go

@@ -319,6 +319,10 @@ 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 err != nil {
+				log.Errorf("Walk func in Query got error: %v", err)
+				return err
+			}
 
 			if !info.Mode().IsRegular() || strings.HasPrefix(info.Name(), ".") {
 				return nil