Reason:
When call function HiiSetString to update the string which has no old string exist for one language, it will failed.
Solution:
When no old string exist, update with new string.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11257 6f19259b-4bc3-4df7-8a09-765794883524