Fix dictionary changing size during iteration

Python3 makes .keys() a view and so del's are working on the dictionary
in the view. Iterate over a copy, rater than the view directly.

Author: SpamapS

src/saml2/filter.py

@@ -21,7 +21,7 @@ def __init__(self, allow):
     def __call__(self, entity_descriptor):
         # get descriptors
         _all = []
-        for desc in entity_descriptor.keys():
+        for desc in list(entity_descriptor.keys()):
             if desc.endswith("_descriptor"):
                 typ, _ = desc.rsplit("_", 1)
                 if typ in self.allow: