When the compositor is canceled mid-execution, the image node will get
corrupt in future executions in new CPU execution mode. That's because
the image node treated cached images as an intermediate results that can
be passed through, while they should be treated as external resources
since they are managed by the static cache manager.
This patch fixes that by adding another variant of wrap_external that
takes a Result and wraps its data, then we use that in the Image node.
1bd64e873e