FIX: error with groups that has no eMailAddress

Signed-off-by: Daniel Bacher <mail@phill93.de>

kitgvapi/models.py

@@ -54,7 +54,8 @@ class Group(Model):
         self.gidNumber = data['gidNumber']
         self.readOnly = data['readOnly']
         self.verteiler = data['verteiler']
-        self.eMailAddress = data['eMailAddress']
+        if 'eMailAddress' in data:
+            self.eMailAddress = data['eMailAddress']
         self.oe_pk = data['oe']
         self.pk = getattr(self, SYMBOLS['GROUP_PK_ATTRIB'])