ERP5Type/patches: prepare for removal of Products.DCWorkflowGraph
Supports the case where Products.DCWorkflowGraph is not present. Even though we are removing Products.DCWorkflowGraph from the software release, we don't remove this monkey patch yet, because this monkey patch also fixed a severe security issue. We keep the patch for the cases where a recent ERP5 runs on an old SlapOS where the product is still there.
This change just moves the existing code in a try/except ImportError block