Avoid rendering when the pipeline is being reset
We should make sure the pipeline is ok before starting a render, otherwise the render gets stuck:
ERROR 07:01:25 pipeline pitivi+utils+pipeline+pipeline0 _async_done_not_received_cb: we didn't get async done, this is a bug (pitivi/utils/pipeline.py:301)
ERROR 07:01:25 pipeline pitivi+utils+pipeline+pipeline0 _recover: Resetting pipeline because error detected during playback. Try 1 (pitivi/utils/pipeline.py:472)
Traceback (most recent call last):
File "/home/aleb/dev/pitivi/pitivi/pitivi/utils/pipeline.py", line 640, in _bus_message_cb
SimplePipeline._bus_message_cb(self, bus, message)
File "/home/aleb/dev/pitivi/pitivi/pitivi/utils/pipeline.py", line 409, in _bus_message_cb
self.simple_seek(position)
File "/home/aleb/dev/pitivi/pitivi/pitivi/utils/pipeline.py", line 613, in simple_seek
raise PipelineError("Trying to seek while rendering")
pitivi.utils.pipeline.PipelineError: Trying to seek while rendering