fix rare race condition

We updated the collection's count before the new value could be retrieved. Between updating the count and actually having something to retrieve was an async call, which allowed the UI thread to retrieve data which was not there.

Author: Trolldemorted

Signal-Windows/Storage/DB.cs

@@ -780,6 +780,7 @@ public static void SaveMessageLocked(SignalMessage message)
 
         public static List<SignalMessageContainer> GetMessagesLocked(SignalConversation thread, int startIndex, int count)
         {
+            Debug.WriteLine($"GetMessagesLocked {thread.ThreadId} {startIndex} {count}");
             lock (DBLock)
             {
                 using (var ctx = new SignalDBContext())

Signal-Windows/ViewModels/MainPageViewModel.cs

@@ -335,7 +335,6 @@ public async Task UIHandleIncomingMessage(SignalMessage message)
             {
                 Debug.WriteLine("incoming lock grabbed");
                 var thread = ThreadsDictionary[message.ThreadId];
-                thread.MessagesCount += 1;
                 uint unreadCount = thread.UnreadCount;
                 if (SelectedThread == thread)
                 {
@@ -346,6 +345,7 @@ await Task.Run(() =>
                     SignalDBContext.SaveMessageLocked(message);
                 });
                 long? seenId = null;
+                thread.MessagesCount += 1;
                 if (SelectedThread == thread)
                 {
                     var container = new SignalMessageContainer(message, (int) thread.MessagesCount - 1);