fixes an exception which occurs when there is no HTTP referer.
fixes an exception which occurs when there is no HTTP referer.

* Issue

When board's post view page is loaded and there is not HTTP referer, an exception occurs.
Because there is no statements checking referer existence.

* Soltuion

Statements checking referer are added.

Private-issue: 2074

brainagenet/yobi,doortts/forked-for-history,doortts/forked-for-history,Limseunghwan/oss,doortts/forked-for-history,Limseunghwan/oss,oolso/yobi,bloodybear/yona,bloodybear/yona,brainagenet/yobi,yona-projects/yona,doortts/fork-yobi,oolso/yobi,ahb0327/yobi,yona-projects/yona,doortts/fork-yobi,yona-projects/yona,yona-projects/yona,bloodybear/yona,naver/yobi,naver/yobi,bloodybear/yona,naver/yobi,ahb0327/yobi,ihoneymon/yobi,ihoneymon/yobi,doortts/fork-yobi,brainagenet/yobi,ihoneymon/yobi,doortts/fork-yobi,ahb0327/yobi,oolso/yobi,Limseunghwan/oss