Reincarnate the last layer even if there is a "fake" reference layer
Otherwise there is a GUI lock happens:
- Add a reference image
- Remove all the layers in the layers docker
(and now you cannot add any new layers :) )
BACKPORT:krita/4.2
(cherry picked from commit 555ad15f39cddf7b4342bacfd1ae447d5fa1f1f6)