Clear undo stack after saving.

--HG--
branch : feature

src/app/mainwindow.cpp

@@ -1645,7 +1645,7 @@ bool MainWindow::SavePattern(const QString &fileName)
         {
             setCurrentFile(fileName);
             helpLabel->setText(tr("File saved"));
-            qApp->getUndoStack()->setClean();
+            qApp->getUndoStack()->clear();
         }
     }
     return result;