Improve checking for nil in nn_list
Improve checking for nil in nn_list

Signed-off-by: Martin Sustrik <4dd6061be1198639e8b05ce4fd5ead7a0dcaa0f4@250bpm.com>

ttyangf/nanomsg,nirs/nanomsg,gdamore/mamomsg,TTimo/nanomsg,wfxiang08/nanomsg,pch957/nanomsg,TTimo/nanomsg,featherweight/ftw-kernel-nanomsg,potatogim/nanomsg,reqshark/nanomsg,zerotacg/nanomsg,krafczyk/nanomsg,yan97ao/nanomsg,hyperfact/nanomsg,cosin2008/nanomsg.NET,simplestbest/nanomsg,tempbottle/nanomsg,TTimo/nanomsg,kaostao/nanomsg,wfxiang08/nanomsg,reqshark/nanomsg,smithed/nanomsg,potatogim/nanomsg,snikulov/nanomsg,JackDunaway/featherweight-nanomsg,cosin2008/nanomsg.NET,potatogim/nanomsg,pch957/nanomsg,linearregression/nanomsg,yan97ao/nanomsg,imp/nanomsg,kaostao/nanomsg,modulexcite/nanomsg,modulexcite/nanomsg,imp/nanomsg,snikulov/nanomsg,smithed/nanomsg,reqshark/nanomsg,ttyangf/nanomsg,zerotacg/nanomsg,zerotacg/nanomsg,JackDunaway/featherweight-nanomsg,pakozm/nanomsg,nirs/nanomsg,simplestbest/nanomsg,hyperfact/nanomsg,wfxiang08/nanomsg,tempbottle/nanomsg,ttyangf/nanomsg,smithed/nanomsg,hyperfact/nanomsg,linearregression/nanomsg,pakozm/nanomsg,gdamore/mamomsg,krafczyk/nanomsg,JackDunaway/featherweight-nanomsg,kaostao/nanomsg,nirs/nanomsg,smithed/nanomsg,pakozm/nanomsg,thisco-de/nanomsg,thisco-de/nanomsg,wirebirdlabs/featherweight-nanomsg,linearregression/nanomsg,featherweight/ftw-kernel-nanomsg,gdamore/mamomsg,kaostao/nanomsg,wirebirdlabs/featherweight-nanomsg,ttyangf/nanomsg,imp/nanomsg,tempbottle/nanomsg,pch957/nanomsg,wirebirdlabs/featherweight-nanomsg,TTimo/nanomsg,yan97ao/nanomsg,simplestbest/nanomsg,modulexcite/nanomsg,krafczyk/nanomsg,cosin2008/nanomsg.NET