Fix crash in getStringSplit.

Summary:
getStringSplit used to crash, when trying to split a long string
literal containing both printable and unprintable multi-byte UTF-8 characters.

Reviewers: djasper, klimek

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D2268

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195728 91177308-0d34-0410-b5e6-96231b3b80d8