gegl filters in batch processing

[pyjamaslug]

All right! That now works, sorry about the random call to pdp-gimp-edge-detect. That was just me trying to find something that might work and forgetting to comment it out when it didn’t. So thanks for reading the code more carefully than I did.
I now need to more fully understand drawables and layers because that missing bit of understanding was what caused me to use the hard coded value that was causing the problem.
Thanks again.