nghttp: Check req is null, found by coverity
nghttp: Check req is null, found by coverity

thinred/nghttp2,serioussam/nghttp2,serioussam/nghttp2,thinred/nghttp2,icing/nghttp2,wzyboy/nghttp2,icing/nghttp2,thinred/nghttp2,thinred/nghttp2,thinred/nghttp2,thinred/nghttp2,serioussam/nghttp2,icing/nghttp2,serioussam/nghttp2,wzyboy/nghttp2,thinred/nghttp2,wzyboy/nghttp2,wzyboy/nghttp2,wzyboy/nghttp2,icing/nghttp2,icing/nghttp2,serioussam/nghttp2,wzyboy/nghttp2,serioussam/nghttp2,icing/nghttp2,wzyboy/nghttp2,serioussam/nghttp2,icing/nghttp2