Fix #35037: Compositor: MultilayerEXR + undo loses image. Crash when selecting in Image Editor

Issue was cause dby ima->ibufs being stored in a ma on
undo/redo and ima->rr not. In case of multilayer image
ibufs hares pointer with render result, so current
undo/redo policy lead to a dead pointer stored in ibuf.

Made it so ima->rr also stores in the map and restores
on redo/undo keeping all the pointers fine.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56201 954f8c5b-7b00-dc11-b283-0030488c597c