Downgrade IGListKit assertion

Summary: This assertion has been firing for at least the [last 3 months](https://fburl.com/scuba/errorreporting_instagram_ios_assertions/vfxo4h2g) and we have shipped the app anyways so it is definitely not launch blocking.

Reviewed By: fabiomassimo

Differential Revision: D49281317

fbshipit-source-id: d525f88fe676e813b8413a2e0f21b6b12728b359

Source/IGListDiffKit/IGListAssert.h

@@ -13,6 +13,10 @@
 #define IGWarn( condition, ... ) NSCAssert( (condition) , ##__VA_ARGS__)
 #endif // IGWarn
 
+#ifndef IGWarnAssert
+#define IGWarnAssert(frmt, ... ) IGAssert( (NO) , ##__VA_ARGS__)
+#endif // IGWarnAssert
+
 #ifndef IGFailAssert
 #define IGFailAssert( ... ) IGAssert( (NO) , ##__VA_ARGS__)
 #endif // IGFailAssert

Source/IGListKit/Internal/IGListBatchUpdateTransaction.m

@@ -143,7 +143,7 @@ - (void)_didDiff:(IGListIndexSetResult *)diffResult onBackground:(BOOL)onBackgro
             [self _reload];
         } else if (self.sectionData && [self.collectionView numberOfSections] != self.sectionData.fromObjects.count) {
             // If data is nil, there are no section updates.
-            IGFailAssert(@"The UICollectionView's section count (%li) didn't match the IGListAdapter's count (%li), so we can't performBatchUpdates. Falling back to reloadData.",
+            IGWarnAssert(@"The UICollectionView's section count (%li) didn't match the IGListAdapter's count (%li), so we can't performBatchUpdates. Falling back to reloadData.",
                          (long)[self.collectionView numberOfSections],
                          (long)self.sectionData.fromObjects.count);
             [self _reload];