Fix duplicate messages in timeline after sending

src/timeline/TimelineModel.cpp

@@ -139,6 +139,17 @@ TimelineModel::TimelineModel(TimelineViewManager *manager, QString room_id, QObj
         });
         connect(this, &TimelineModel::messageSent, this, [this](QString txn_id, QString event_id) {
                 pending.removeOne(txn_id);
+
+                // we could have received the message via sync
+                if (events.contains(event_id)) {
+                        int idx = idToIndex(event_id);
+                        if (idx >= 0) {
+                                beginRemoveRows(QModelIndex(), idx, idx);
+                                eventOrder.erase(eventOrder.begin() + idx);
+                                endRemoveRows();
+                        }
+                }
+
                 int idx = idToIndex(txn_id);
                 if (idx < 0) {
                         nhlog::ui()->warn("Sent index out of range");