Fix timeline preview failing when creating a new project

Related to #993

src/timeline2/view/timelinecontroller.cpp

@@ -103,6 +103,7 @@ void TimelineController::setModel(std::shared_ptr<TimelineItemModel> model)
     m_lastVideoTarget = -1;
     m_lastAudioTarget.clear();
     m_timelinePreview = nullptr;
+    m_usePreview = false;
     m_model = std::move(model);
     m_activeSnaps.clear();
     connect(m_model.get(), &TimelineItemModel::requestClearAssetView, pCore.get(), &Core::clearAssetPanel);