Fixed typo in error dialog

ui/main_window.py

@@ -235,7 +235,7 @@ class MainWindow(QMainWindow):
 
         options = QFileDialog.Options()
         filename, _ = QFileDialog.getSaveFileName(
-            self.dialog, 'QFileDialog.getSaveFileName()', '', ext,
+            self, 'QFileDialog.getSaveFileName()', '', ext,
             options=options)
 
         if filename: