graphics/gegl: update to 0.4.38 release (+)

Operations:
~~~~~~~~~~

• denoise-dct: a NEW denoising operation which decomposes the input buffer to

sliding overlapping patches, calculates the DCT denoising in each patch, and
then aggregates the denoised patches to the output buffer averaging the
overlapped pixels.

• ff-load and ff-save: big cleanup API cleanup, now ffmpeg-5.0 compatible
• gif-load: updated to latest upstream libnsgif version
• slic: progress reporting and improved parameter handling.
• vector-fill: updated to latest upstream ctx version
• oilify: clamp inputs to avoid nan in output
• gegl:load fix possible double free
• rgbe-write: plug leaks in error paths

Core:
~~~~

Fixes of some potential NULL dereferences on custom dataformats for malformed
inputs.