Fix filename parsing

For filenames that need more information, such as the same mealcard from
both of us, it was replacing the cc information.

pfbudget/utils.py

@@ -44,7 +44,7 @@ def find_credit_institution(fn, banks, creditcards):
         except ValueError:
             if not bank:
                 bank = i
-            else:
+            elif not cc:
                 cc = i
 
     if not bank: