[mob][photos] Don't let syncing trigger another sync

mobile/lib/events/people_changed_event.dart

@@ -19,4 +19,5 @@ class PeopleChangedEvent extends Event {
 enum PeopleEventType {
   defaultType,
   removedFilesFromCluster,
+  syncDone,
 }

mobile/lib/services/machine_learning/face_ml/face_ml_service.dart

@@ -194,6 +194,7 @@ class FaceMlService {
 
   void _listenOnPeopleChangedSync() {
     Bus.instance.on<PeopleChangedEvent>().listen((event) {
+      if (event.type == PeopleEventType.syncDone) return;
       _shouldSyncPeople = true;
     });
   }
@@ -367,7 +368,7 @@ class FaceMlService {
     _isSyncing = true;
     if (forceSync) {
       await PersonService.instance.reconcileClusters();
-      Bus.instance.fire(PeopleChangedEvent());
+      Bus.instance.fire(PeopleChangedEvent(type: PeopleEventType.syncDone));
       _shouldSyncPeople = false;
     }
     _isSyncing = false;