Cycles: Assert in the cases when SVM node was not handled

This will help figuring out cases when node was not properly handled by the SVM
by aborting execution on CPU, where all the nodes are expected to be supported.

intern/cycles/kernel/svm/svm.h

@@ -448,7 +448,9 @@ ccl_device_noinline void svm_eval_nodes(KernelGlobals *kg, ShaderData *sd, Shade
 #  endif  /* __EXTRA_NODES__ */
 #endif  /* NODES_GROUP(NODE_GROUP_LEVEL_3) */
 			case NODE_END:
+				return;
 			default:
+				kernel_assert(!"Unknown node type was passed to the SVM machine");
 				return;
 		}
 	}