[CollectionView] Guard against a UIKit crash caused by attempting to …

…scroll to an item that no longer exists (#142)

Calling `scrollToItem(…)` with in invalid index path raises an exception:

> NSInternalInconsistencyException: Attempted to scroll the collection view to an out-of-bounds item

We must guard against this to check to ensure that this never happens, as we call this method repeatedly and the items/section may change out from under us.

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   insets as they may be incorrect.
 - Pass initial size to embedded view from `CollectionViewCell`/`CollectionViewReusableView` to 
   better load embedded SwiftUI views.
+- Guard against a UIKit crash caused by attempting to scroll to an item that no longer exists.
 
 ## [0.9.0](https://github.com/airbnb/epoxy-ios/compare/0.8.0...0.9.0) - 2022-10-25
 

Sources/EpoxyCollectionView/CollectionView/Internal/CollectionViewScrollToItemHelper.swift

@@ -154,12 +154,25 @@ final class CollectionViewScrollToItemHelper {
   {
     self.scrollToItemContext = nil
 
-    collectionView?.scrollToItem(
-      at: scrollToItemContext.targetIndexPath,
-      at: scrollToItemContext.targetScrollPosition,
-      animated: animated)
+    guard let collectionView = collectionView else { return }
+
+    // Calling `scrollToItem(…)` with in invalid index path raises an exception:
+    // > NSInternalInconsistencyException: Attempted to scroll the collection view to an out-of-
+    // >  bounds item
+    // We must guard against this to check to ensure that this never happens, as we call this method
+    // repeatedly and the items/section may change out from under us.
+    if
+      case let indexPath = scrollToItemContext.targetIndexPath,
+      indexPath.section < collectionView.numberOfSections,
+      indexPath.item < collectionView.numberOfItems(inSection: indexPath.section)
+    {
+      collectionView.scrollToItem(
+        at: indexPath,
+        at: scrollToItemContext.targetScrollPosition,
+        animated: animated)
+    }
 
-    if let collectionView = collectionView, !animated {
+    if !animated {
       collectionView.delegate?.scrollViewDidEndScrollingAnimation?(collectionView)
     }
   }