all: Ignore Sync errors on directories (fixes #4432)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4449

lib/fs/basicfs.go

@@ -317,22 +317,6 @@ func (f fsFile) Stat() (FileInfo, error) {
 	return fsFileInfo{info}, nil
 }
 
-func (f fsFile) Sync() error {
-	err := f.File.Sync()
-	if err == nil || runtime.GOOS != "windows" {
-		return err
-	}
-	// On Windows, fsyncing a directory returns a "handle is invalid" (localized so can't check for strings)
-	// So we swallow that and let things go through in order not to have to add
-	// a separate way of syncing directories versus files.
-	if stat, serr := f.Stat(); serr != nil {
-		return serr
-	} else if stat.IsDir() {
-		return nil
-	}
-	return err
-}
-
 // fsFileInfo implements the fs.FileInfo interface on top of an os.FileInfo.
 type fsFileInfo struct {
 	os.FileInfo