Fix crash

SignalUtilitiesKit/Messaging/OWSMessageUtils.m

@@ -72,11 +72,13 @@ NS_ASSUME_NONNULL_BEGIN
     [LKStorage readWithBlock:^(YapDatabaseReadTransaction *transaction) {
         YapDatabaseViewTransaction *unreadMessages = [transaction ext:TSUnreadDatabaseViewExtensionName];
         NSArray<NSString *> *allGroups = [unreadMessages allGroups];
+        // FIXME: Confusingly, `allGroups` includes contact threads as well
         for (NSString *groupID in allGroups) {
-            TSGroupThread *thread = [TSGroupThread fetchObjectWithUniqueID:groupID transaction:transaction];
-            if (thread.isMuted) continue;
+            TSThread *thread = [TSThread fetchObjectWithUniqueID:groupID transaction:transaction];
+            if (thread.isMuted) { continue; }
+            BOOL isGroupThread = thread.isGroupThread;
             [unreadMessages enumerateKeysAndObjectsInGroup:groupID
-                                                usingBlock:^(NSString *collection, NSString *key, id object, NSUInteger index, BOOL *stop) {
+                usingBlock:^(NSString *collection, NSString *key, id object, NSUInteger index, BOOL *stop) {
                 if (![object conformsToProtocol:@protocol(OWSReadTracking)]) {
                     return;
                 }
@@ -85,9 +87,11 @@ NS_ASSUME_NONNULL_BEGIN
                     NSLog(@"Found an already read message in the * unread * messages list.");
                     return;
                 }
-                TSIncomingMessage * incomingMessage = (TSIncomingMessage *)object;
-                if (incomingMessage != nil && thread.isOnlyNotifyingForMentions && !incomingMessage.isUserMentioned) {
-                    return;
+                if ([object isKindOfClass:TSIncomingMessage.class] && isGroupThread) {
+                    TSIncomingMessage *incomingMessage = (TSIncomingMessage *)object;
+                    if (((TSGroupThread *)thread).isOnlyNotifyingForMentions && !incomingMessage.isUserMentioned) {
+                        return;
+                    }
                 }
                 count += 1;
             }];