Fix long conversation crash the right way

Session/Conversations/ConversationVC.swift

@@ -149,7 +149,8 @@ final class ConversationVC : BaseVC, ConversationViewModelDelegate, OWSConversat
         Storage.read { transaction in
             unreadCount = self.thread.unreadMessageCount(transaction: transaction)
         }
-        unreadViewItems = unreadCount != 0 ? [ConversationViewItem](viewItems[viewItems.endIndex - Int(unreadCount) ..< viewItems.endIndex]) : []
+        let clampedUnreadCount = min(unreadCount, UInt(kConversationInitialMaxRangeSize))
+        unreadViewItems = clampedUnreadCount != 0 ? [ConversationViewItem](viewItems[viewItems.endIndex - Int(clampedUnreadCount) ..< viewItems.endIndex]) : []
     }
     
     required init?(coder: NSCoder) {

Session/Conversations/ConversationViewModel.h

@@ -91,6 +91,24 @@ typedef NS_ENUM(NSUInteger, ConversationUpdateItemType) {
 
 #pragma mark -
 
+// Always load up to n messages when user arrives.
+//
+// The smaller this number is, the faster the conversation can display.
+// To test, shrink you accessibility font as much as possible, then count how many 1-line system info messages (our
+// shortest cells) can fit on screen at a time on an iPhoneX
+//
+// PERF: we could do less messages on shorter (older, slower) devices
+// PERF: we could cache the cell height, since some messages will be much taller.
+static const int kYapDatabasePageSize = 250;
+
+// Never show more than n messages in conversation view when user arrives.
+static const int kConversationInitialMaxRangeSize = 250;
+
+// Never show more than n messages in conversation view at a time.
+static const int kYapDatabaseRangeMaxLength = 250;
+
+#pragma mark -
+
 @interface ConversationViewModel : NSObject
 
 @property (nonatomic, readonly) ConversationViewState *viewState;

Session/Conversations/ConversationViewModel.m

@@ -162,24 +162,6 @@ NS_ASSUME_NONNULL_BEGIN
 
 #pragma mark -
 
-// Always load up to n messages when user arrives.
-//
-// The smaller this number is, the faster the conversation can display.
-// To test, shrink you accessibility font as much as possible, then count how many 1-line system info messages (our
-// shortest cells) can fit on screen at a time on an iPhoneX
-//
-// PERF: we could do less messages on shorter (older, slower) devices
-// PERF: we could cache the cell height, since some messages will be much taller.
-static const int kYapDatabasePageSize = 25000;
-
-// Never show more than n messages in conversation view when user arrives.
-static const int kConversationInitialMaxRangeSize = 25000;
-
-// Never show more than n messages in conversation view at a time.
-static const int kYapDatabaseRangeMaxLength = 25000;
-
-#pragma mark -
-
 @interface ConversationViewModel ()
 
 @property (nonatomic, weak) id<ConversationViewModelDelegate> delegate;

SignalUtilitiesKit/Utilities/ThreadUtil.m

@@ -198,6 +198,14 @@ NS_ASSUME_NONNULL_BEGIN
                                 visibleUnseenMessageCount++;
 
                                 interactionAfterUnreadIndicator = interaction;
+        
+                                if (visibleUnseenMessageCount + 1 >= maxRangeSize) {
+                                    // If there are more unseen messages than can be displayed in the
+                                    // messages view, show the unread indicator at the top of the
+                                    // displayed messages.
+                                    *stop = YES;
+                                    hasMoreUnseenMessages = YES;
+                                }
                             }];
 
     if (!interactionAfterUnreadIndicator) {