fuse mount: avoid lookup nil entry

fix https://github.com/chrislusf/seaweedfs/issues/1221

weed/s3api/s3api_bucket_handlers.go

@@ -13,6 +13,7 @@ import (
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/gorilla/mux"
 
+	"github.com/chrislusf/seaweedfs/weed/filer2"
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
 )
@@ -117,7 +118,10 @@ func (s3a *S3ApiServer) HeadBucketHandler(w http.ResponseWriter, r *http.Request
 		}
 
 		glog.V(1).Infof("lookup bucket: %v", request)
-		if resp, err := client.LookupDirectoryEntry(context.Background(), request); err != nil || resp.Entry == nil {
+		if _, err := filer_pb.LookupEntry(client, request); err != nil {
+			if err == filer2.ErrNotFound {
+				return filer2.ErrNotFound
+			}
 			return fmt.Errorf("lookup bucket %s/%s: %v", s3a.option.BucketsPath, bucket, err)
 		}