Fix a potential wild pointer error when markSlotSuccessful comes late am: 65e8b6c195 am: f22fa83e8e

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1663460

Change-Id: I3f166238a920086316de1b5ab4eac7775ba87b41
diff --git a/aosp/cleanup_previous_update_action.cc b/aosp/cleanup_previous_update_action.cc
index b447509..ae2727a 100644
--- a/aosp/cleanup_previous_update_action.cc
+++ b/aosp/cleanup_previous_update_action.cc
@@ -207,6 +207,7 @@
   if (!kIsRecovery &&
       !boot_control_->IsSlotMarkedSuccessful(boot_control_->GetCurrentSlot())) {
     ScheduleWaitMarkBootSuccessful();
+    return;
   }
 
   if (metadata_device_ == nullptr) {