Issue #11931: Include filters when composing
This patch attempts to resolve the updated issue in #11931 (closed) (since c6d38fa5 resolves the initial problem)
Since we use gimp_drawable_get_buffer ()
to get the
pixel data when composing or recomposing, NDE filters
were not being included in the final output.
This patch temporarily duplicates the layer, merges the filters, and then retrieves the GeglBuffer from the merged version of the layer rather than the raw pixels.