Fix adding account when none were previously saved

src/backend/user_files.py

@@ -192,10 +192,10 @@ class Accounts(JSONDataFile):
                 "token":      client.access_token,
                 "device_id":  client.device_id,
                 "enabled":    True,
-                "order":      max(
+                "order":      max([
                     account.get("order", i)
                     for i, account in enumerate(saved.values())
-                ) + 1,
+                ] or [-1]) + 1,
             },
         })