Merge pull request #288 from ruslanskorb/list-monitor-number-of-objects-performance

[ListMonitor] Fix performance of `numberOfObjects()`.

Sources/ListMonitor.swift

@@ -232,7 +232,7 @@ public final class ListMonitor<D: DynamicObject>: Hashable {
             !self.isPendingRefetch || Thread.isMainThread,
             "Attempted to access a \(cs_typeName(self)) outside the main thread while a refetch is in progress."
         )
-        return self.fetchedResultsController.fetchedObjects?.count ?? 0
+        return (self.fetchedResultsController.fetchedObjects as NSArray?)?.count ?? 0
     }
     
     /**