Clearer comment

Signed-off-by: James Hewitt <james.hewitt@uk.ibm.com>

registry/storage/driver/walk.go

@@ -46,9 +46,9 @@ func doWalkFallback(ctx context.Context, driver StorageDriver, from string, star
 	for _, child := range children {
 		// (@jamstah) This will still walk objects that are before the startAfterHint,
 		// but to avoid that we would need to cache top level folders to check if there
-		// are any children then call the WalkFn, which is extra overhead. As the
-		// hint is just a hint for performance reasons, its fine to walk the extra
-		// objects instead.
+		// are any valid children then call the WalkFn for the cached entries only if
+		// there are, which is extra overhead. Because the hint is just a hint for
+		// performance reasons, its fine to walk the extra objects instead.
 		if child < startAfterHint && !strings.HasPrefix(startAfterHint, child) {
 			continue
 		}