Fix Infinite loop  of UCharacter.toUpperCase for GREEK

CaseMapImpl.isFollowedByCasedLetter() must increment the string index while looping
Patch from public http://bugs.icu-project.org/trac/changeset/40353

Test: UCharacterCaseTest
Bug: 64998746
Change-Id: I5578274cf799411250485494a112614ab5ce8c99
5 files changed