AttributeError: 'NoneType' object has no attribute 'isPaused'

[rimach]

Tested with trunk Version 880.

After starting preview of a Powerpoint presentation with impress, I get the following error at the commandline.

Traceback (most recent call last):
  File "F:\Computer\Platform\pythonDev\openlp\trunk\openlp\plugins\presentations\lib\messagelistener.py", line 255, in slide
    self.preview_handler.slide(slide, item)
  File "F:\Computer\Platform\pythonDev\openlp\trunk\openlp\plugins\presentations\lib\messagelistener.py", line 77, in slide
    if self.doc.is_blank():
  File "F:\Computer\Platform\pythonDev\openlp\trunk\openlp\plugins\presentations\lib\impresscontroller.py", line 330, in is_blank
    return self.control.isPaused()
AttributeError: 'NoneType' object has no attribute 'isPaused'

Anyway, preview seems to be work correctly.