Prevent deallocation of asyncDataSource and asyncDelegate in ASCollectionView and ASTableView

Grab a strong reference for asyncDataSource and asyncDelegate in ASCollectionView and ASTableView before executing the range update to be sure they are not going away while executing the range update. This can happen in range updates while going back in the view controller hierarchy

AsyncDisplayKit/Details/ASRangeController.mm

@@ -27,6 +27,7 @@
   BOOL _didUpdateCurrentRange;
   BOOL _didRegisterForNotifications;
   CFAbsoluteTime _pendingDisplayNodesTimestamp;
+  NSMutableArray *_scheduledRangeUpdateCompletionBlocks;
 }
 
 @end
@@ -46,6 +47,7 @@ static UIApplicationState __ApplicationState = UIApplicationStateActive;
   _rangeIsValid = YES;
   _currentRangeMode = ASLayoutRangeModeInvalid;
   _didUpdateCurrentRange = NO;
+  _scheduledRangeUpdateCompletionBlocks = [NSMutableArray array];
   
   [[[self class] allRangeControllersWeakSet] addObject:self];
   
@@ -111,6 +113,15 @@ static UIApplicationState __ApplicationState = UIApplicationStateActive;
 
 - (void)scheduleRangeUpdate
 {
+  [self scheduleRangeUpdateCompletion:nil];
+}
+
+- (void)scheduleRangeUpdateCompletion:(void (^)(void))completion
+{
+  if (completion) {
+    [_scheduledRangeUpdateCompletionBlocks addObject:completion];
+  }
+ 
   if (_queuedRangeUpdate) {
     return;
   }
@@ -118,8 +129,13 @@ static UIApplicationState __ApplicationState = UIApplicationStateActive;
   // coalesce these events -- handling them multiple times per runloop is noisy and expensive
   _queuedRangeUpdate = YES;
   
+  __block id<ASRangeControllerDataSource> dataSource = _dataSource;
+  __block id<ASRangeControllerDelegate> delegate = _delegate;
   dispatch_async(dispatch_get_main_queue(), ^{
-    [self performRangeUpdate];
+    [self _updateVisibleNodeIndexPaths];
+    
+    dataSource = nil;
+    delegate = nil;
   });
 }
 
@@ -320,6 +336,11 @@ static UIApplicationState __ApplicationState = UIApplicationStateActive;
   _rangeIsValid = YES;
   _queuedRangeUpdate = NO;
   
+  for (void (^completionBlock)(void) in _scheduledRangeUpdateCompletionBlocks) {
+    completionBlock();
+  }
+  [_scheduledRangeUpdateCompletionBlocks removeAllObjects];
+  
 #if ASRangeControllerLoggingEnabled
 //  NSSet *visibleNodePathsSet = [NSSet setWithArray:visibleNodePaths];
 //  BOOL setsAreEqual = [visibleIndexPaths isEqualToSet:visibleNodePathsSet];