Fix T68457: Cycles OpenCL Displacement Shading

When doing simple scenes the displacement shading failed during final
rendering when the displacement method is set to `Displacement + Bump`.

When this option is enabled the shader uses the Vector math
node. This node is part of the node group level 1. When doing simple
shading only using nodes that are part of the node group level
0 the shading was rendered black.

This only happened in final rendering as there the OpenCL programs are
optimized to save registries. Viewport rendering rendered correctly

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D5859

intern/cycles/render/shader.cpp

@@ -703,6 +703,7 @@ void ShaderManager::get_requested_features(Scene *scene,
       requested_features->nodes_features |= NODE_FEATURE_BUMP;
       if (shader->displacement_method == DISPLACE_BOTH) {
         requested_features->nodes_features |= NODE_FEATURE_BUMP_STATE;
+        requested_features->max_nodes_group = max(requested_features->max_nodes_group,  NODE_GROUP_LEVEL_1);
       }
     }
     /* On top of volume nodes, also check if we need volume sampling because