UserApp: Fix server error caused by OptimisticLockException
UserApp: Fix server error caused by OptimisticLockException

OptimisticLockException occurred occasionally when
UserApp.updatePreferredLanguage() is called.

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