Complaint about missing SVG when duplicating workflow

[matthias-ronge]

If you want to duplicate a workflow and the SVG file for the workflow is missing in the diagrams folder, an error message is issued and it is not possible to duplicate the workflow. However, at this point the SVG file of the template workflow is not needed. When saving the duplicated workflow, a new SVG will be written with the correct content.

Goal: When duplicating a workflow, the file does not have to be checked for existence.