Currently, the Render mode of the GPU Cryptomatte mode extracts the
Cryptomatte layers based on information in the RenderResult of the
scene. This means the node will not work if no RenderResult exists,
which is typically the case for the viewport compositor, and especially
after #123378.
To fix this, we simply acquire the passes directly from the appropriate
view layer based on the node's layer name. The render compositor context
implementation will handle the extraction from the RenderResult, while
the viewport compositor will just return the DRW passes.
Pull Request: https://projects.blender.org/blender/blender/pulls/123817
862028f4dc