component AP gateway: fix header checking for redirection

sat/plugins/plugin_comp_ap_gateway/http_server.py

@@ -942,7 +942,7 @@ class HTTPAPGServer(web_resource.Resource):
             path
         )
         request_type, extra_args = self.apg.parseAPURL(ap_url)
-        if ((request.getHeader("accept") != MEDIA_TYPE_AP
+        if ((MEDIA_TYPE_AP in (request.getHeader("accept") or "")
              and request_type in self.apg.html_redirect)):
             # this is not a AP request, and we have a redirections for it
             kw = {}