fix update queueing when using reload fallback

Summary: If we fallback to `reloadData`, we don't queue the next update. That means if you call `performUpdate` multiple times quickly, there's a chance that the last update doesn't take effect.

Reviewed By: Haud

Differential Revision: D22219237

fbshipit-source-id: 167e3428859a0194f8f8c57624504edd531480df

CHANGELOG.md

@@ -18,6 +18,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Fixed `IGListAdapterUpdaterDelegate` by 1) calling `willReloadDataWithCollectionView` on fallback reloads and 2) making sure `willPerformBatchUpdatesWithCollectionView` is only called when performing a batch update. [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
+- Fixed missing update when calling `performUpdatesAnimated` multiple times quickly and using the `reloadDataFallback()`. [Maxime Ollivier](https://github.com/maxolls) (tbd)
+
 4.0.0
 -----
 ### Breaking Changes

Source/IGListKit/IGListAdapterUpdater.m

@@ -179,6 +179,10 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
         [collectionView layoutIfNeeded];
         executeCompletionBlocks(YES);
         [delegate listAdapterUpdater:self didReloadDataWithCollectionView:collectionView isFallbackReload:YES];
+
+        // queue another update in case something changed during batch updates. this method will bail next runloop if
+        // there are no changes
+        [self _queueUpdateWithCollectionViewBlock:collectionViewBlock];
     };
 
     // disables multiple performBatchUpdates: from happening at the same time