fix crash in is_simple_http_request

Under some conditions is_simple_http_request access lf->url unchecked. If lf->url is null, it will segfault.
Merge pull request #232 from navtej/master

fix crash in is_simple_http_request

Under some conditions is_simple_http_request access lf->url unchecked. If lf->url is null, it will segfault.