providers/os: Fix incorrect return value count

providers/os/os.go

@@ -148,12 +148,12 @@ func (this *state) funcWriteFile (name, content string) error {
 
 func (this *state) countFiles(name string) (int, error) {
 	name, err := this.document.Rel(name)
-	if err != nil { return err }
+	if err != nil { return 0, err }
 	// genuinely can't believe this is the only way to do it, we have to
 	// read their names and everything, all that work just to know how many
 	// files there are, its slightly upsetting
 	files, err := os.ReadDir(name)
-	if err != nil { return err }
+	if err != nil { return 0, err }
 	return len(files), nil
 }