Exception reported when presentation sent to preview
To reproduce:
Add a presentation (eg impress) into the Library Presentations section.
Click on the presentation and then Preview the selected presentation.
Openlp reports an exception:
\Users\Robbie\Downloads\openlp\openlp\openlp\core\ui\slidecontroller.py", line 945, in _process_item [self.service_item, self.is_live, self._current_hide_mode, slide_no]) AttributeError: 'PreviewController' object has no attribute '_current_hide_mode