Error when cleaning image behind us

[julien-duponchelle]

Traceback (most recent call last):
  File "/Users/noplay/code/gns3/gns3-server/gns3server/web/route.py", line 200, in control_schema
    yield from func(request, response)
  File "/Users/noplay/code/gns3/gns3-server/gns3server/handlers/api/controller/project_handler.py", line 234, in notification
    yield from project.close()
  File "/Users/noplay/code/gns3/gns3-server/gns3server/controller/project.py", line 502, in close
    self._cleanPictures()
  File "/Users/noplay/code/gns3/gns3-server/gns3server/controller/project.py", line 515, in _cleanPictures
    pictures.remove(drawing.ressource_filename)
KeyError