Handle pure django users in userinfo endpoint

Any user that does not have a GregUserProfile must be a superuser so
this is not a problem per se, but it should be handled. For now we
simply treat them as an anonymous user and deny access.

Resolves: GREG-116

gregui/api/views/userinfo.py

@@ -39,7 +39,10 @@ class UserInfoView(APIView):
 
         # Authenticated user, allow access
         if user.is_authenticated:
-            user_profile = GregUserProfile.objects.get(user=user)
+            try:
+                user_profile = GregUserProfile.objects.get(user=user)
+            except GregUserProfile.DoesNotExist:
+                return Response(status=HTTP_403_FORBIDDEN)
             sponsor_id = None
             person_id = None
             if user_profile.sponsor: