handlers/room_member: fix guest access check when joining rooms

Signed-off-by: Patrik Oldsberg <patrik.oldsberg@ericsson.com>

synapse/handlers/room_member.py

@@ -232,7 +232,9 @@ class RoomMemberHandler(BaseHandler):
         is_host_in_room = yield self._is_host_in_room(current_state_ids)
 
         if effective_membership_state == Membership.JOIN:
-            if requester.is_guest and not self._can_guest_join(current_state_ids):
+            if requester.is_guest:
+                guest_can_join = yield self._can_guest_join(current_state_ids)
+                if not guest_can_join:
                     # This should be an auth check, but guests are a local concept,
                     # so don't really fit into the general auth process.
                     raise AuthError(403, "Guest access not allowed")