Fails if reconstruction `method = none`

If config file field reconstruction/method is set to none (as suggested in doc string), process fails with:

...
Taking logarithm
Saving data
Traceback (most recent call last):
  File "/home/esrf/lesaint/envs/ub2004_x86/bin/nabu", line 8, in <module>
    sys.exit(main())
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/app/reconstruct.py", line 114, in main
    R.reconstruct()
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/reconstruction.py", line 611, in reconstruct
    self._reconstruct_chunked()
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/reconstruction.py", line 564, in _reconstruct_chunked
    self.pipeline.process_chunk(task["sub_region"])
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/chunked.py", line 845, in process_chunk
    self._process_chunk()
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/chunked.py", line 814, in _process_chunk
    self._write_data()
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/chunked_cuda.py", line 134, in _write_data
    super()._write_data(data=data)
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/utils.py", line 34, in wrapper
    res = func(*args, **kwargs)
  File "/home/esrf/lesaint/envs/ub2004_x86/lib/python3.8/site-packages/nabu/pipeline/fullfield/chunked.py", line 755, in _write_data
    data = self.recs
AttributeError: 'CudaChunkedPipeline' object has no attribute 'recs'