only visit nodes in EnumerateChildrenAsync when asked

No idea why this was changed this was introduced in:

08f342e8bada4f4eb0c5462a3623f0c2b828240f (part of #3598)

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

merkledag.go

@@ -319,17 +319,17 @@ func EnumerateChildrenAsync(ctx context.Context, getLinks GetLinks, c *cid.Cid,
 	for i := 0; i < FetchGraphConcurrency; i++ {
 		go func() {
 			for ic := range feed {
+				setlk.Lock()
+				shouldVisit := visit(ic)
+				setlk.Unlock()
+
+				if shouldVisit {
 					links, err := getLinks(ctx, ic)
 					if err != nil {
 						errChan <- err
 						return
 					}
 
-				setlk.Lock()
-				unseen := visit(ic)
-				setlk.Unlock()
-
-				if unseen {
 					select {
 					case out <- links:
 					case <-fetchersCtx.Done():