Update first & last sender after message deletion

fixes #282

include/timeline/TimelineView.h

@@ -154,8 +154,11 @@ private:
         TimelineEvent findFirstViewableEvent(const std::vector<TimelineEvent> &events);
         TimelineEvent findLastViewableEvent(const std::vector<TimelineEvent> &events);
 
+        //! Mark the last event as read.
         void readLastEvent() const;
+        //! Whether or not the scrollbar is visible (non-zero height).
         bool isScrollbarActivated() { return scroll_area_->verticalScrollBar()->value() != 0; }
+        //! Retrieve the event id of the last item.
         QString getLastEventId() const;
         QString getEventSender(const mtx::events::collections::TimelineEvents &event) const;
         mtx::events::EventType getEventType(

src/timeline/TimelineView.cc

@@ -753,6 +753,20 @@ TimelineView::removeEvent(const QString &event_id)
                 prevLabel->deleteLater();
         }
 
+        // If we deleted the last item in the timeline...
+        if (!nextItem && prevItem)
+                lastSender_ = prevItem->descriptionMessage().userid;
+
+        // If we deleted the first item in the timeline...
+        if (!prevItem && nextItem)
+                firstSender_ = nextItem->descriptionMessage().userid;
+
+        // If we deleted the only item in the timeline...
+        if (!prevItem && !nextItem) {
+                firstSender_.clear();
+                lastSender_.clear();
+        }
+
         // Finally remove the event.
         removedItem->deleteLater();
         eventIds_.remove(event_id);