Fix list item initialization and removeal in astream.
Fix list item initialization and removeal in astream.

astream was not initializing its list item and was trying to remove the
item before the item was added to the list.

This fix one type of crash during tcp_shutdown test.

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

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