Reset the sender's name when paginating backwards

The first message of the timeline would have an avatar and
the rest of the messages would use the previous to be configured
(whether or not should have an avatar).

fixes #63

src/TimelineView.cc

@@ -179,6 +179,10 @@ TimelineView::addBackwardsEvents(const QString &room_id, const RoomMessages &msg
         isTimelineFinished = false;
         QList<TimelineItem *> items;
 
+        // Reset the sender of the first message in the timeline
+        // cause we're about to insert a new one.
+        firstSender_.clear();
+
         // Parse in reverse order to determine where we should not show sender's
         // name.
         auto ii = msgs.chunk().size();