add login check for first request execution

src/delta_barth/api/requests.py

@@ -66,6 +66,11 @@ def get_sales_prognosis_data(
         BuchungsDatum=start_date,
     )
     empty_response = SalesPrognosisResponse(daten=tuple())
+    if not session.logged_in:
+        _, status = session.login()
+        if status != STATUS_HANDLER.SUCCESS:
+            return empty_response, status
+
     resp: Response | None = None
     try:
         for attempt in range(1, (MAX_LOGIN_RETRIES + 1)):