Deezer provider is not downloading tracks

[gnuletik]

When importing an item with the Deezer provider:

• the Task succeeds

• The encoder fails with

  self.source = aubio.source(self.uri, hop_size=self.output_blocksize)
  TypeError: argument 1 must be str, not None

  See https://github.com/Parisson/TimeSide/issues/202

• The ItemTranscode route fails with a 500 error and this exception

ValueError at /timeside/api/items/e0e7b9fe-7056-4760-9cd7-33456e92f38f/download/ogg
The 'file' attribute has no file associated with it.

[gnuletik]

Duplicate of https://github.com/Parisson/TimeSide/issues/206