Fix crash in exception handler

Direct use of k['kid'] was causing the excpetion itself to
crash on keys that do not have a 'kid' with a keyError.

Always use the .get accessor to pull 'kid' so that None is
returned when not availble.

Fixes #209

Signed-off-by: Simo Sorce <simo@redhat.com>

jwcrypto/jwk.py

@@ -1183,6 +1183,6 @@ def get_key(self, kid):
         :param kid: the 'kid' key identifier.
         """
         for jwk in self['keys']:
-            if jwk['kid'] == kid:
+            if jwk.get('kid') == kid:
                 return jwk
         return None

jwcrypto/jwt.py

@@ -491,7 +491,7 @@ def deserialize(self, jwt, key=None):
                         self.deserializelog.append("Success")
                         break
                     except Exception as e:  # pylint: disable=broad-except
-                        keyid = k['kid']
+                        keyid = k.get('kid')
                         if keyid is None:
                             keyid = k.thumbprint()
                         self.deserializelog.append('Key [%s] failed: [%s]' % (