Fix of the encryption processing with the Student class

Web/app.py

@@ -4431,10 +4431,19 @@ def student_card_class_barcode_download():
         db = client[cfg.MONGODB_DB]
         student_cards = db['student_cards']
 
-        class_cards = list(student_cards.find({'Klasse': class_name}).sort('AusweisId', 1))
-        class_cards = [_decrypt_student_card_doc(card) for card in class_cards]
+        # 1. Alle Ausweise laden
+        all_cards = list(student_cards.find().sort('AusweisId', 1))
         client.close()
 
+        # 2. Alle entschlüsseln
+        decrypted_cards = [_decrypt_student_card_doc(card) for card in all_cards]
+        
+        # 3. Im Speicher nach der Klartext-Klasse filtern
+        class_cards = [
+            card for card in decrypted_cards 
+            if card.get('Klasse', '').strip() == class_name
+        ]
+
         if not class_cards:
             flash(f'Keine Ausweise für die Klasse "{class_name}" gefunden.', 'error')
             return redirect(url_for('student_cards_admin'))