- WebPPictureImportRGB(A)() docs say these functions return "false in
case of memory error". Handle such cases.
- status was not updated when WebPEncode() would fail in save_layer().
- gegl_buffer_flush() is unnecessary just before last unref-ing GEGL
buffers. This is done automatically at destruction.
- Destroy resources at the same level as they were created if possible.
This makes the code more readable and maintainable. Consequently
better not unref parameter GEGL buffers inside combine_buffers().
- Some minor formatting cleanup.
c5edf05cf0