googlephotos: fix crash with --gphotos-batch-mode async

Before this change the async batch mode would return a nil info and we
attempted to use it and crashed.

The whole idea of async mode is that we don't wait for the response so
this patch ignores the empty info.

Fixes #8233

backend/googlephotos/googlephotos.go

@@ -1193,7 +1193,12 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		return fmt.Errorf("failed to commit batch: %w", err)
 	}
 
-	o.setMetaData(info)
+	// Store the info back into the Object
+	// info == nil will only happen if we are uploading async batches
+	// we don't have anything sensible to write into the info then.
+	if info != nil {
+		o.setMetaData(info)
+	}
 
 	// Add upload to internal storage
 	if pattern.isUpload {