Fix for out of bounds on last seen search

Fixes #6661
Fixes #6660
// FREEBIE

src/org/thoughtcrime/securesms/ConversationAdapter.java

@@ -314,7 +314,7 @@ public class ConversationAdapter <V extends View & BindableConversationItem>
     if (lastSeen <= 0)     return -1;
     if (!isActiveCursor()) return -1;
 
-    int count = getItemCount();
+    int count = getItemCount() - (hasHeaderView() ? 1 : 0) - (hasFooterView() ? 1 : 0);
 
     for (int i=0;i<count;i++) {
       MessageRecord messageRecord = getRecordForPositionOrThrow(i);