Only use an open handle during the traversal section, not while waiting for subdirs

drive-demuxer.go

@@ -274,6 +274,7 @@ func (s *Step) AreFilesIdentical(child string) bool {
 func (s *Step) Walk() {
 	wg := sync.WaitGroup{}
 
+	s.OpenHandles <- 1
 	children := s.ListChildren()
 	s.Bar.AddTotal(int64(len(children)))
 	for _, child := range children {
@@ -328,10 +329,8 @@ func (s *Step) Walk() {
 				wg.Add(1)
 				go func() {
 					defer func() {
-						<-s.OpenHandles
 						wg.Done()
 					}()
-					s.OpenHandles <- 1
 					substep.Walk()
 					s.RemoveInputDirs(child)
 					s.Bar.Increment()
@@ -345,6 +344,7 @@ func (s *Step) Walk() {
 		}
 	}
 
+	<-s.OpenHandles
 	wg.Wait()
 }