Pamhyr: Fix tests and pep8.

src/Model/River.py

@@ -355,7 +355,10 @@ class River(Graph, SQLSubModel):
         )
 
     def _db_save_delete_artefact_where_not_id(self, execute, data,
-                                              table:str, els:list):
+                                              table: str, els: list):
+        if len(els) == 0:
+            return
+
         try:
             execute(
                 f"DELETE FROM {table} " +