Perform actions before parent main window is closed.

def closing_plugin(self, cancelable=False):
        """Perform actions before parent main window is closed."""
        if self.busy:
            answer = QMessageBox.question(
                self,
                'Conda Manager',
                'Conda Manager is still busy.\n\nDo you want to quit?',
                buttons=QMessageBox.Yes | QMessageBox.No)

            if answer == QMessageBox.Yes:
                return True
            else:
                return False
        else:
            return True