Fix timeline thumbnails not saved with project

src/timeline2/view/timelinecontroller.cpp

@@ -3587,8 +3587,8 @@ QStringList TimelineController::getThumbKeys()
     for (const auto &clp : m_model->m_allClips) {
         const QString binId = getClipBinId(clp.first);
         std::shared_ptr<ProjectClip> binClip = pCore->bin()->getBinClip(binId);
-        result << binClip->hash() + QLatin1Char('#') + QString::number(clp.second->getIn()) + QStringLiteral(".png");
-        result << binClip->hash() + QLatin1Char('#') + QString::number(clp.second->getOut()) + QStringLiteral(".png");
+        result << binClip->hash() + QLatin1Char('#') + QString::number(clp.second->getIn()) + QStringLiteral(".jpg");
+        result << binClip->hash() + QLatin1Char('#') + QString::number(clp.second->getOut()) + QStringLiteral(".jpg");
     }
     result.removeDuplicates();
     return result;