Only check last directory when discovering checkpoint number (#5756)

* Only check last directory when discovering checkpoint number

Signed-off-by: Devin Trejo <dtrejo@palantir.com>

* Comments for checkpointNum

Signed-off-by: Devin Trejo <dtrejo@palantir.com>

storage/remote/wal_watcher.go

@@ -526,7 +526,8 @@ func (w *WALWatcher) readCheckpoint(checkpointDir string) error {
 
 func checkpointNum(dir string) (int, error) {
 	// Checkpoint dir names are in the format checkpoint.000001
-	chunks := strings.Split(dir, ".")
+	// dir may contain a hidden directory, so only check the base directory
+	chunks := strings.Split(path.Base(dir), ".")
 	if len(chunks) != 2 {
 		return 0, errors.Errorf("invalid checkpoint dir string: %s", dir)
 	}