[ios] Remove bookmark model from observer list.

iphone/Maps/Bookmarks/Categories/BMCView/BMCViewController.swift

@@ -42,20 +42,19 @@ final class BMCViewController: MWMViewController {
 
   override func viewDidAppear(_ animated: Bool) {
     super.viewDidAppear(animated)
-    
     // Disable all notifications in BM on appearance of this view.
     // It allows to significantly improve performance in case of bookmarks
     // modification. All notifications will be sent on controller's disappearance.
     viewModel.setNotificationsEnabled(false)
-    
+    viewModel.addToObserverList()
     viewModel.convertAllKMLIfNeeded()
   }
   
   override func viewDidDisappear(_ animated: Bool) {
     super.viewDidDisappear(animated)
-    
     // Allow to send all notifications in BM.
     viewModel.setNotificationsEnabled(true)
+    viewModel.removeFromObserverList()
   }
 
   private func updateCategoryName(category: BMCCategory?) {

iphone/Maps/Bookmarks/Categories/BMCViewModel/BMCDefaultViewModel.swift

@@ -222,6 +222,14 @@ extension BMCDefaultViewModel: BMCViewModel {
   func areNotificationsEnabled() -> Bool {
     return BM.areNotificationsEnabled()
   }
+
+  func addToObserverList() {
+    BM.add(self)
+  }
+
+  func removeFromObserverList() {
+    BM.remove(self)
+  }
 }
 
 extension BMCDefaultViewModel: MWMBookmarksObserver {