Fix a bug in GetOptionalStringByIndex() that doesn't handle the case when Index == 0.
Code is re-organized to be more readable and simpler.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10823 6f19259b-4bc3-4df7-8a09-765794883524
1 file changed