BUG: Removed a video and the application crashed #33

It printed this:

File "/home/manuel/projects/pythonVideoAnnotator/libraries/pyforms-gui/pyforms_gui/controls/control_player/control_player.py", line 105, in refresh
frame = self.process_frame_event(self._currentFrame.copy())
File "/home/manuel/projects/pythonVideoAnnotator/libraries/mcv-gui/mcvgui/dialogs/simple_filter/simple_filter.py", line 142, in __process_frame
frame_index = self._player.video_index-1
TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'
Aborted (core dumped)