Fix crash with 'select all' in conversation list.

Fixes #9790

app/src/main/java/org/thoughtcrime/securesms/conversationlist/ConversationListAdapter.java

@@ -213,7 +213,7 @@ class ConversationListAdapter extends PagedListAdapter<Conversation, RecyclerVie
   }
 
   void selectAllThreads() {
-    for (int i = 0; i < getItemCount(); i++) {
+    for (int i = 0; i < super.getItemCount(); i++) {
       Conversation conversation = getItem(i);
       if (conversation != null && conversation.getThreadRecord().getThreadId() != -1) {
         batchSet.put(conversation.getThreadRecord().getThreadId(), conversation);