Issue #4209: Animation optimize for GIF moves layers to top left corner.

Regression from commit 9d33a9a9 as spotted by Massimo.

(cherry picked from commit 9a4d1f02)
3 jobs for gimp-2-10 in 18 minutes and 34 seconds (queued for 1 second)
Status Job ID Name Coverage
  Babl
passed #509600
babl-git

00:02:12

 
  Gegl
passed #509601
gegl-git

00:05:41

 
  Gimp
passed #509602
build-git-autotools

00:10:40