Some fixes for CUDA runtime compile:

* When Baking wasn't used we got an error.
* On top of Volume Nodes (NODES_FEATURE_VOLUME), we now also check if we need volume sampling code,
so we can disable that as well and save some further compilation time.

intern/cycles/render/shader.cpp

@@ -528,6 +528,10 @@ void ShaderManager::get_requested_features(Scene *scene,
 		if(output_node->input("Displacement")->link != NULL) {
 			requested_features->nodes_features |= NODE_FEATURE_BUMP;
 		}
+		/* On top of volume nodes, also check if we need volume sampling because
+		 * e.g. an Emission node would slip through the NODE_FEATURE_VOLUME check */
+		if(shader->has_volume)
+			requested_features->use_volume |= true;
 	}
 }