fix the exporter of the qt viewer

tools/assimp_qt_viewer/mainwindow.cpp

@@ -295,7 +295,7 @@ aiReturn rv;
 
 	// begin export
 	time_begin = QTime::currentTime();
-	rv = exporter.Export(mScene, format_id.toLocal8Bit(), filename.toLocal8Bit());
+	rv = exporter.Export(mScene, format_id.toLocal8Bit(), filename.toLocal8Bit(), aiProcess_FlipUVs);
 	ui->lblExportTime->setText(QString("%1").arg(time_begin.secsTo(QTime::currentTime())));
 	if(rv == aiReturn_SUCCESS)
 		LogInfo("Export done: " + filename);