check directory permission

src/gui/edit_tandem_preset_dialog/edittandempresetdialog.cpp

@@ -103,7 +103,11 @@ void EditTandemPresetDialog::doSelectDir() {
 
         QString directory = QFileDialog::getExistingDirectory(this,tr("Choose preset directory"),_preset_directory );
 
+        QFileInfo my_dir(directory);
         if (!directory.isEmpty() && ! directory.isNull()) {
+            if (!my_dir.isWritable()) {
+                throw pappso::PappsoException(QObject::tr("this directory is not writable, check permissions (%1)").arg(my_dir.absoluteFilePath()));
+            }
             _preset_directory = directory;
             fillPresetComboBox();
         }