don't resolve children unnecessarily when listing a sharded directory

We only need to get the child if it's a shard.

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

unixfs/hamt/hamt.go

@@ -289,13 +289,13 @@ func (ds *Shard) loadChild(ctx context.Context, i int) (child, error) {
 		return nil, fmt.Errorf("invalid link name '%s'", lnk.Name)
 	}
 
+	var c child
+	if len(lnk.Name) == ds.maxpadlen {
 		nd, err := lnk.GetNode(ctx, ds.dserv)
 		if err != nil {
 			return nil, err
 		}
 
-	var c child
-	if len(lnk.Name) == ds.maxpadlen {
 		pbnd, ok := nd.(*dag.ProtoNode)
 		if !ok {
 			return nil, dag.ErrNotProtobuf