[#1070] services/tree: Fix fast listing depth processing

For unsorted `GetSubTree()` we return a single node for depth=1.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/services/tree/service.go

@@ -456,28 +456,23 @@ func getSortedSubTree(ctx context.Context, srv TreeService_GetSubTreeServer, cid
 		return err
 	}
 
-	err = srv.Send(&GetSubTreeResponse{
-		Body: &GetSubTreeResponse_Body{
-			NodeId:    b.GetRootId(),
-			ParentId:  p,
-			Timestamp: m.Time,
-			Meta:      metaToProto(m.Items),
-		},
-	})
-	if err != nil {
-		return err
-	}
-
 	stack := []stackItem{{
-		values: nil,
-		parent: b.GetRootId(),
-		last:   "",
+		values: []pilorama.NodeInfo{{
+			ID:       b.GetRootId(),
+			Meta:     m,
+			ParentID: p,
+		}},
+		parent: p,
 	}}
 
 	for {
 		if len(stack) == 0 {
 			break
 		} else if item := &stack[len(stack)-1]; len(item.values) == 0 {
+			if len(stack) == 1 {
+				break
+			}
+
 			nodes, last, err := forest.TreeSortedByFilename(ctx, cid, b.GetTreeId(), item.parent, item.last, batchSize)
 			if err != nil {
 				return err