Fix missing_token for Flask client

This may fix #448

authlib/integrations/base_client/sync_app.py

@@ -79,7 +79,7 @@ def _send_token_request(self, session, method, url, token, kwargs):
         if withhold_token:
             return session.request(method, url, **kwargs)
 
-        if token is None and self._fetch_token:
+        if token is None:
             token = self._get_requested_token(request)
 
         if token is None: