Fixed issue #537. Valentina crashes when use undo command.

(grafted from b9726acb2bb6b7bd606d6ecc96e6498f093c1861)

--HG--
branch : develop

src/app/valentina/mainwindow.cpp

@@ -2445,6 +2445,7 @@ void MainWindow::Clear()
     qt_ntfs_permission_lookup--; // turn it off again
 #endif /*Q_OS_WIN32*/
     qApp->getUndoStack()->clear();
+    toolOptions->ClearPropertyBrowser();
     toolOptions->itemClicked(nullptr);
 }