We used to generate textures multiple times for each worker process,
which didn't seem to be intended as it was done gated behind a reversed
if statement. It just so happened to fix an issue introduced by the
pickling code which was deleting vital attributes like the actual
generated textures.
I'm honestly not sure why this was ever done, so let's just throw this
out and call it a day.
Fixes#1728
Nicolas F
9895fe875b