[Fix] False as multi_step default in legacy API (#406)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#406

epdb/legacy_api.py

@@ -2059,7 +2059,7 @@ def add_pathway_edge(request, package_uuid, pathway_uuid, e: Form[CreateEdge]):
             for pr in e.products.split(","):
                 products.append(Node.objects.get(pathway=pw, url=pr.strip()))
 
-        multi_step = None
+        multi_step = False
         if e.multistep and e.multistep.strip() == "true":
             multi_step = True