[Fix] Iuclid export produce only one root substance (#429)

Reviewed-on: enviPath/enviPy#429
Co-authored-by: Tobias O <tobias.olenyi@envipath.com>
Co-committed-by: Tobias O <tobias.olenyi@envipath.com>

epiuclid/serializers/pathway_mapper.py

@@ -120,13 +120,6 @@ class PathwayMapper:
             )
             bundle.reference_substances.append(ref_sub)
 
-            sub = IUCLIDSubstanceData(
-                uuid=sub_uuid,
-                name=compound.name,
-                reference_substance_uuid=ref_sub_uuid,
-            )
-            bundle.substances.append(sub)
-
         if not export.compounds:
             return bundle
 
@@ -145,6 +138,16 @@ class PathwayMapper:
         if not root_compound_pks:
             return bundle
 
+        for root_pk in root_compound_pks:
+            root_sub_uuid, root_ref_uuid = seen_compounds[root_pk]
+            bundle.substances.append(
+                IUCLIDSubstanceData(
+                    uuid=root_sub_uuid,
+                    name=compound_names[root_pk],
+                    reference_substance_uuid=root_ref_uuid,
+                )
+            )
+
         edge_templates: list[tuple[UUID, frozenset[int], tuple[int, ...], tuple[UUID, ...]]] = []
         for edge in sorted(export.edges, key=lambda item: str(item.edge_uuid)):
             parent_compound_pks = sorted(