Adjust last seen divider on read sync

Fixes #6273
// FREEBIE

src/org/thoughtcrime/securesms/database/MmsDatabase.java

@@ -524,6 +524,7 @@ public class MmsDatabase extends MessagingDatabase {
               database.update(TABLE_NAME, values, ID_WHERE, new String[]{String.valueOf(id)});
 
               DatabaseFactory.getThreadDatabase(context).updateReadState(threadId);
+              DatabaseFactory.getThreadDatabase(context).setLastSeen(threadId);
               notifyConversationListeners(threadId);
             }
           } catch (InvalidNumberException e) {

src/org/thoughtcrime/securesms/database/SmsDatabase.java

@@ -383,6 +383,7 @@ public class SmsDatabase extends MessagingDatabase {
             database.update(TABLE_NAME, contentValues, ID_WHERE, new String[] {cursor.getLong(cursor.getColumnIndexOrThrow(ID)) + ""});
 
             DatabaseFactory.getThreadDatabase(context).updateReadState(threadId);
+            DatabaseFactory.getThreadDatabase(context).setLastSeen(threadId);
             notifyConversationListeners(threadId);
           }
         } catch (InvalidNumberException e) {