Fix 100% CPU when EDIT_TIME=0 in image cleanup

When EditDuration is zero or negative, cleanupTTL becomes zero,
causing time.After(0) to fire immediately in a tight loop.
Block on ctx.Done() instead when edit duration is disabled. Fixes #1991

backend/app/store/image/image.go

@@ -154,6 +154,12 @@ func (s *Service) ExtractNonProxiedPictures(commentHTML string) (ids []string) {
 
 // Cleanup runs periodic cleanup with 1.5*ServiceParams.EditDuration. Blocking loop, should be called inside of goroutine by consumer
 func (s *Service) Cleanup(ctx context.Context) {
+	if s.EditDuration <= 0 {
+		log.Printf("[INFO] pictures cleanup disabled, edit duration is %v", s.EditDuration)
+		<-ctx.Done()
+		return
+	}
+
 	cleanupTTL := s.EditDuration * 15 / 10 // cleanup images older than 1.5 * EditDuration
 	log.Printf("[INFO] start pictures cleanup, staging ttl=%v", cleanupTTL)